Small Muscle Research Articles

Skeletal Muscle Oxygen Delivery and Utilization during Exercise in Heart Failure with Preserved Ejection Fraction: Role of Sympathetic (α‐adrenergic) Vasoconstriction

BACKGROUNDHeart Failure with preserved ejection fraction (HFpEF) is characterized by severe exercise intolerance underpinned by low aerobic capacity (VO2peak). It is likely low VO2peak in HFpEF is not only related to deficits in cardiac function, but also peripheral vascular and skeletal muscle dysfunction that may disrupt the balance between O2 delivery and utilization. There is emerging evidence for sympathetic nervous system overactivity in patients with HFpEF that results in excessive vasoconstriction in the peripheral circulation, and may therefore contribute to dysregulation of exercising muscle blood flow. We tested the hypothesis that pharmacological blockade of sympathetic (α‐adrenergic) vasoconstriction would increase blood flow, O2 delivery and utilization of exercising skeletal muscle to a greater extent in HFpEF compared to healthy control subjects.METHODSFour healthy control (CON) (2 M, 69±3 yrs) and three HFpEF (1 M, 71±3) volunteers participated in this study. Femoral blood flow (FBF) was assessed by ultrasound Doppler. Catheters were placed in the femoral artery and vein for drug infusions and determination of arterial and venous O2 content (CaO2 and CvO2, respectively). O2 utilization of the exercising leg was calculated via the Fick equation: VO2 = FBF∙(CaO2‐CvO2), and O2 delivery was calculated as FBF∙CaO2. Measurements were made at rest and during dynamic single‐leg knee‐extension (KE) exercise (5 W) before and after intra‐arterial infusion of the α‐adrenergic antagonist phentolamine (PHEN).RESULTSBaseline FBF, O2 delivery, and VO2 were similar between groups. At rest, PHEN increased FBF and O2 delivery similarly in both groups, while the increase in VO2 tended to be smaller in patients with HFpEF compared to CON (+3±2 vs. +14±5 ml/min; respectively, P=0.09). During KE exercise, a ≍20‐30% decrement in FBF (2052±261 vs. 2529±230 ml/min; HFpEF vs. CON, P=0.23), O2 delivery (282±27 vs. 392±35 ml/min, HFpEF vs. CON, P=0.07), and VO2 (193±25 vs. 284±31 ml/min; HFpEF vs. CON, P=0.09) were observed in patients with HFpEF. PHEN increased exercising muscle FBF (+243±45 vs. +247±58 ml/min; HFpEF vs. CON) and O2 delivery (+51±9 vs. +34±19 ml/min; HFpEF vs. CON) similarly between groups, while the PHEN‐induced increase in VO2 tended to be greater in patients with HFpEF (+20±12 vs. +6±7 ml/min; HFpEF vs. CON, P=0.32).CONCLUSIONTaken together, these preliminary data suggest a reduction in FBF, O2 delivery and utilization during small muscle mass exercise in patients with HFpEF that may be, in part but not fully, explained by excessive sympathetic (α‐adrenergic) vasoconstriction in this patient group.

Localized Heat Therapy Improves Mitochondrial Respiratory Capacity but Not Fat Oxidation in Human Skeletal Muscle

Exercise training (EX) imposes stress on skeletal muscle, resulting in improved mitochondrial respiratory capacity and fat oxidation. Heat, which is one of the stresses of exercise, has been previously shown to increase mitochondrial respiration in human skeletal muscle. Still, it is unknown how the effects of localized heat therapy (HEAT) compare to the effects of EX, or if HEAT improves fat oxidation capacity. Therefore, the objective of this study was to determine the extent to which 6 weeks of HEAT improve mitochondrial function compared to EX. We hypothesized that HEAT would increase mitochondrial respiratory capacity, fatty acid oxidation and citrate synthase (CS) activity, but to a lesser extent than EX. Subjects were randomized into three groups: HEAT (n=11), EX (n=8), and a sham control group (CON, n=12). Subjects in the HEAT group were exposed to 2 hrs/day, 3 days/wk of short‐wave diathermy, which raised internal muscle temperature by 3.2 ± 0.33° C, while CON subjects experienced no change in muscle temperature during sham diathermy sessions. EX consisted of single‐leg extension exercise on a modified cycle ergometer for 45 min/day, 3 days/week, and resulted in a 1.8 ± 0.42° C increase in muscle temperature. Muscle biopsies were performed at baseline, and after 3 and 6 weeks of intervention. Small muscle fiber bundles (2‐4 mg wet wt.) were permeabilized, and mitochondrial respiration was assessed using high‐resolution respirometry (Oroboros O2k, Innsbruck, Austria). CS and 3‐hydroxyacyl‐CoA dehydrogenase (HAD) activity assays were performed in duplicate on supernatant from homogenized muscle samples. At 6 weeks, EX resulted in 27.9 ± 8.7% and 33.2 ± 11.7% increases in maximal coupled and uncoupled respiration, respectively, which were significantly different from baseline (p<0.05). At 6 weeks, HEAT resulted in 24.8 ± 6.2% and 24.5 ± 6.2% increases in maximal coupled and uncoupled respiration, respectively, which were significantly different from baseline (p<0.05), but not different from EX. Fatty acid oxidation was improved only in EX subjects after 6 weeks (29.5 ± 6.8%), compared to baseline (p<0.05), with no change in HEAT or CON subjects. CS activity increased in EX subjects (25.9 ± 10.5 µmol·min‐1·mg protein‐1 or 19.0 ± 7.4%) compared to all others (p<0.05), but no changes were observed in HEAT or CON subjects. Furthermore, no change in HAD activity occurred in any group. These results suggest that HEAT improves mitochondrial respiratory capacity to a similar extent as EX but does not result in other EX‐induced adaptations like increased fat oxidation and CS activity. Still, HEAT‐induced improvements in respiratory capacity may have therapeutic potential in the context of skeletal muscle disease or disuse, and further investigation is warranted.

P042 Spontaneous gallbladder perforation: a rare complication of eosinophilic granulomatosis with polyangiitis

Abstract Background/Aims Gallbladder (GB) perforation is a serious clinical condition, caused by cholecystitis with or without cholelithiasis. Although there have been reports of bowel perforation in many cases of vasculitis, we report to the best of our knowledge, the first case of spontaneous gallbladder perforation following a diagnosis of EGPA. This alerts the clinician to a unique complication of EGPA. Methods A 48-year-old man presented initially to haematology with weight loss and marked eosinophilia, investigations (bone marrow aspirate and trephine, CT chest, abdomen and pelvis) at the time showed no evidence of haematological causes. Subsequently, he developed worsening weakness and paraesthesia of the upper and lower limbs, ongoing for 4 months. He had a background of asthma, and hay fever, which were well-controlled. On examination, he had progressive quadriparesis with extensive muscle wasting. His abdomen was soft non-tender, and he had no skin changes, although he later revealed a photograph of a vasculitic rash affecting the limbs when the symptoms initially presented. Results Laboratory findings revealed raised white blood cells of 46.9 (4-10 x109/L), raised eosinophils of 29.4 (0.01-0.5 x109/L), thrombocytosis of 757 (150-410 x109/L), raised CRP of 172 (0-10mg/L), raised IgE 179(<107 kU/L), and IgG 20.8(6-16 g/L). An extensive infectious screen was performed including HIV, and hepatitis (A-E), which were all negative. Vasculitic screen was negative for PR3 and MPO ANCA. However, nerve conduction studies showed evidence of confluent mononeuritis mimicking acute demyelinating sensory motor neuropathy. Following this, a CT scan was requested to exclude underlying neoplasms and infection which revealed a GB perforation with defect in the distended GB wall. He had no typical symptoms of cholecystitis, favouring an underlying gallbladder necrotizing vasculitis as the cause of GB perforation. The patient was commenced on IV cyclophosphamide and maintained on prednisolone, and azathioprine. A percutaneous cholecystostomy was inserted and immunosuppression continued with antibiotic cover. He had excellent response to therapy and his mobility improved following physiotherapy and rehabilitation. However, he continues to have significant residual weakness of the small muscles of his hand (median and ulnar nerve palsies). An MRCP was later requested, this revealed a contracted GB with no evidence of cholelithiasis or ongoing inflammation. He remained asymptomatic of GB perforation, and as a result, surgeons decided not to proceed with a cholecystectomy. Conclusion Gallbladder vasculitis (GV) can occur as a single organ vasculitis or as part of a systemic vasculitis. In the rare occasion of its occurrence, it mainly presents as symptoms of cholecystitis. Spontaneous GB perforation as a complication of GV has been noted in patients with other vasculitides like Henoch-Schonlein Purpura. However, this is the first report of a spontaneous gallbladder perforation in a patient with EGPA. Disclosure J. Ochogwu: None. A. Madathil: None. H. Mazin: None. D. Makkuni: None.

Skeletal muscle coverage in undergraduate courses: a comparison of stand-alone human anatomy and anatomy and physiology (A&P) courses.

Anecdotal data suggest great variation in breadth and depth of skeletal muscle coverage between undergraduate human anatomy (HA) and anatomy and physiology (A&P) courses. This manuscript is the second in a series (Reynolds A, Goodwin M, O'Loughlin VD. Adv Physiol Educ 46: 309-318, 2022. doi:https://doi.org/10.1152/advan.00084.2021) that methodically assesses skeletal muscle content coverage across undergraduate HA and A&P courses. The authors developed an online skeletal muscle coverage survey and collected 342 responses worldwide, 156 from instructors of HA courses and 186 from A&P course instructors. Demographic results showed that HA courses are primarily taught at 4-year baccalaureate institutions, have relatively larger class sizes, and are more likely to use human (vs. animal) prosections or dissections. In contrast, A&P courses are primarily taught at community colleges, have relatively smaller class sizes, and are more likely to use animal (vs. human) dissections. HA courses tend to require their students to learn all skeletal muscle aspects (i.e., identification, action, attachments, innervation), whereas A&P courses tend to focus on muscle identification or action only. The proportions of courses that require identification of large, superficial skeletal muscles are similar between the two course types. However, HA courses are more likely to require their students to identify deeper and smaller muscles, including more distal appendicular muscles and pelvic muscles. These differences likely are due, in part, to the more anatomical focus of HA courses and the slightly different student populations between these courses. These findings provide much-needed information about muscular system coverage between HA and A&P courses and may guide instructor discussions about curricula.

Flexor digitorum brevis utilizes elastic strain energy to contribute to both work generation and energy absorption at the foot.

ABSTRACTThe central nervous system utilizes tendon compliance of the intrinsic foot muscles to aid the foot's arch spring, storing and returning energy in its tendinous tissues. Recently, the intrinsic foot muscles have been shown to adapt their energetic contributions during a variety of locomotor tasks to fulfil centre of mass work demands. However, the mechanism by which the small intrinsic foot muscles are able to make versatile energetic contributions remains unknown. Therefore, we examined the muscle–tendon dynamics of the flexor digitorum brevis during stepping, jumping and landing tasks to see whether the central nervous system regulates muscle activation magnitude and timing to enable energy storage and return to enhance energetic contributions. In step-ups and jumps, energy was stored in the tendinous tissue during arch compression; during arch recoil, the fascicles shortened at a slower rate than the tendinous tissues while the foot generated energy. In step-downs and landings, the tendinous tissues elongated more and at greater rates than the fascicles during arch compression while the foot absorbed energy. These results indicate that the central nervous system utilizes arch compression to store elastic energy in the tendinous tissues of the intrinsic foot muscles to add or remove mechanical energy when the body accelerates or decelerates. This study provides evidence for an adaptive mechanism to enable the foot's energetic versatility and further indicates the value of tendon compliance in distal lower limb muscle–tendon units in locomotion.

The distribution of neuromuscular junctions depends on muscle pennation, when botulinum neurotoxin receptors and SNAREs expression are uniform in the rat

Botulinum neurotoxins (BoNTs) are used to treat spastic disorders. Depending on muscle size, one or multiple injections are recommended according to labels to target neuromuscular junctions (NMJ). However, information about NMJ distribution and number in muscles, as well as expression of receptors and molecular targets of toxins is scarce in human and animal models.Seven muscles from adult rats were used to identify expression of BoNT receptors and SNAREs using immunohistochemistry (IHC), and fluorescent α-Bungarotoxin combined to light-sheet microscopy used to determine their distribution.The location, number, and density of NMJ were muscle specific and mostly dependent on the type of pennation (myofiber orientation). In the Flexor Digitorum Brevis (a very small muscle) NMJ were as numerous as in the Gastrocnemius lateralis. A strong expression of SV2C, Synaptotagmin 2, SNAP25 and VAMP1 were observed in all muscles, and SV2A, Synaptotagmin 1 and VAMP2 were never detected.This work highlights the specific distribution of NMJ in muscles which seems to depend on the type of pennation. Detailed observation of myofibers organization might help clinicians to better evaluate the location of NMJ in humans; the molecular phenotyping of NMJ will contribute to better integrate the rat model into research of BoNT therapeutics.

The optimized quantum dot mediated thermometry reveals isoform specific differences in efficiency of myosin extracted from muscle mini bundles

The biophysical function of myosin in vitro has been extensively investigated in different motility assays, but the study of myosin ATPase properties at the fiber level is insufficiently investigated. In this study, quantum dot (QD) mediated thermometry measurements were optimized to measure the efficiency of myosin extracted from muscle mini bundles. A reduction in fluorescent intensity of QD reflects an increase in temperature caused by the heat released during ATP hydrolysis and denotes the efficiency of the motor protein myosin. The procedure for extracting myosin was similar to the single fiber in vitro motility assay with some small modifications, and the concentration of myosin was represented by the extracted total protein since the ratio of extracted myosin to total protein was constant. Moreover, the efficiencies of myosin extracted from preparations containing different myosin heavy chain isoforms reveal lower efficiency of slow compared to fast myosin isoforms. Specifically, more heat was released in slow myosin enzymatic reaction, resulting in faster decay of QD fluorescence intensity. Hence, the optimized QD mediated thermometry provides a novel and sensitive approach to evaluate efficiency of myosin ATPase obtained from small muscle samples, representing a significant advantage in the clinical evaluation of neuromuscular disorders.

Evaluation of spasmolytic effects of naringenin on ileum contraction and intestinal charcoal meal transit: Involvement of ATP-sensitive K+ channels

Introduction: Naringenin is a flavonoid constituent of many herbal plants, including citreous fruits. Biological studies have suggested various therapeutic effects for naringenin, including protective effects on gastrointestinal (GI) motility. The present study was performed to investigate the involvement of ATP-sensitive K+ channels on the effect of naringenin in rat ileum motility. Methods: Ileum contractions were induced by either KCl or acetylcholine (ACh) in vitro. Inhibitory concentration-response curves were constructed for naringenin and diazoxide after exposure of rat isolated ileum to KCl (20mM) or ACh (500nM). The relaxant effects of naringenin and diazoxide were also examined in the presence of glibenclamide. Furthermore, oral effects of diazoxide (25 mg/kg) and naringenin (25, 50 mg/kg) were also assessed on the intestinal charcoal meal transit in mice (n=10) in the absence and presence of glibenclamide (50 mg/kg). Results: Diazoxide and naringenin in a concentration-dependent manner inhibited ileum contractions induced by low bath concentration of KCl (20mM). However, both drugs had no effect on contractions induced by a high concentration of KCl (160mM). The inhibitory effects of diazoxide and naringenin were blocked by glibenclamide. Oral administration of diazoxide and naringenin significantly reduced the intestinal transit of charcoal meal. The delay in the intestinal transit was blocked by the oral dose of glibenclamide. The effect of naringenin on the rat intestinal strip pre-contracted with the KCl was relatively similar to that of ATP-sensitive K+ channel opener (diazoxide). Conclusion: This research supports that ATP-sensitive K+ channels are involved in the rat small intestinal smooth muscles relaxation induced by naringenin.

Improving Early Childhood Fine Motor Development Through Weaving Activities

Early childhood fine motor development can be obtained through supportive learning media. One of them is with paper media. Children can crumple the paper and make patterns on paper with paper media. In this study, the use of writing as a medium is used for weaving activities from articles. In addition to utilizing form as a learning medium, weaving activities are an Indonesian cultural heritage that must be introduced to the next generation early. This research is a class action research, while the object is carried out on 25 RA children in Lampung. The results of this study indicate that most children's motor skills can develop as expected (BSH) through weaving activities with paper in children. Weaving activities can train children's skills in coordinating their eyes and hands, especially finger movements, to stimulate skills in controlling actions involving small or delicate muscles.

"Guys with Big Muscles Have Misplaced Priorities": Masculinities and Muscularities in Young South Korean Men's Body Image.

Men’s body image is an issue of increasing importance as related illnesses continue to grow in prevalence around the world. However, cross-cultural attention to men’s body image experiences has been relatively understudied. Based on data derived from cognitive anthropological methods of cultural domain analysis, I develop the concept of “muscularities” to more effectively examine the expectations inherent in multifarious models of body image men continuously navigate. Related to but distinct from “masculinities”—the recognition of culture-bound hierarchies of ways of doing-being a man—“muscularities” attends to the culturally particular ways in which muscles are conceived and evaluated as indices of socioeconomic status, intelligence, social skills, and professionalism, to name a few. Young South Korean men’s experiences of chan’gŭnyuk (“small muscle”) and manŭn kŭnyuk (“large muscle”) challenge universalist assumptions about the kinds of muscles people value in global perspective, demonstrate the necessity of recognizing multiple muscularities in research, and encourage new directions of inquiry that attend to the consequences of variable embodiments of muscularities.

THE DEEP HIP MUSCLES CAN REDIRECT HIP LOADING AWAY FROM COMMONLY DAMAGED AREAS OF THE ACETABULAR CARTILAGE

Purpose: Cartilage damage around the acetabular rim is common in individuals with hip pathology. Redirecting hip loading away from commonly damaged areas of cartilage to non-degenerated areas of cartilage may be desirable for individuals with hip pathology. The deep hip muscles are a group of small muscles that may be best suited to make small changes to the direction of hip loading. These muscles have limited torque generating capacity, suggesting changes in the direction of hip loading could be achieved without substantially affecting hip motion.

A Simple Model to Predict Loads within Muscle-Tendon Complexes of the Shoulder during Fast Motions

The load scenario within the shoulder joint among its muscle–tendon complexes during fast motions is of interest, as it would allow an evaluation of critical, accident-like motions. To enhance knowledge, a modelling approach was carried out and compared to experimental data. Nine subjects were investigated while performing tasks that ranged from easy to demanding. Motions were (1) an easy lift of a small weight, (2) a push against a force measurement device, and (3) a gentle side fall against the immovable force measurement device. Extracted data were the kinematics of the right arm and the contact force on the elbow. A simple direct dynamics shoulder model actuated by Hill-type muscle models was arranged to simulate the three experimental motions. The Hatze-based activation of the muscle models was used without any further simulation of neural regulation. For fast motions, the simple shoulder model predicts well the shoulder angle or contact force values, and data fit well into the variability of the data measured experimentally. Because there was no implementation of more complex neural regulation, slow motions, as performed by the subjects, were, in part, not predicted by the shoulder model. Simple mechanisms can be described by the simple model: When activated, the larger deltoid muscle is able to protect the smaller supraspinatus muscle. Furthermore, in awkward conditions, the gentle side fall against an immovable device alone has enough momentum to damage small muscles.

Renal Abnormalities Caused by Canine Distemper Virus Infection in Terminal Patients.

The aim of this study was to analyze the glomerular and tubular alterations in dogs with terminal distemper through light microscopy, immunofluorescence, and electron microscopy. Thirteen animals with a molecular diagnosis of distemper and neurological signs were selected. As a control group, 10 clinically healthy animals with no manifestations or signs of disease and with negative tests for Ehrlichia sp., Anaplasma sp., and Babesia sp. were included in this study. Renal tissue was evaluated by light microscopy, topochemistry for DNA/chromatin, and video image analysis to detect the nuclear phenotypes of the renal tubular epithelial cells (RTECs), immunofluorescence, and transmission electron microscopy. Results showed that dogs with distemper exhibited anemia, hypergammaglobulinemia, and proteinuria. Creatinine in the distemper group was lower compared to the control group (p = 0.0026), but there was no significant difference in relation to urea (p = 0.9876). Although this alteration may be due to the smaller muscle mass observed in animals with distemper, it probably is not of clinical importance. Glomerular and tubular lesions were confirmed by light microscopy in 84.6% of these animals. Additional findings in the animals with distemper included deposition of different classes of immunoglobulins, particularly IgM in 92.3% of the cases, fibrinogen deposition in 69.2% of the cases as assessed by immunofluorescence, alterations in the nuclear phenotypes of the RTEC characterized by condensation of chromatin, loss of DNA and reduction in the nuclear shape, and the presence of subendothelial and mesangial electron-dense deposits. These findings confirm the existence of renal alterations related to terminal distemper.

The Efficacy and Safety of Phase I Cardiac Rehabilitation in Patients Hospitalized in Cardiac Intensive Care Unit With Acute Decompensated Heart Failure: A Study Protocol for a Randomized, Controlled, Clinical Trial.

BackgroundCardiac rehabilitation (CR) improves outcomes in patients with heart failure. However, data on CR efficacy in patients with acute decompensated heart failure is limited. This study is designed to assess the efficacy and safety of CR in patients hospitalized in cardiac intensive care unit (CICU) with acute decompensated heart failure (ADHF).MethodsThis is a single-center, randomized controlled, single-blind clinical trial. A total of 120 participants hospitalized in CICU with ADHF will be randomly allocated in the ratio of 1:1 to two groups: CR group and control group. Participants will receive tailored and progressive CR intervention or attention control. The CR intervention include personalized breathing training, small muscle group resistance training, and aerobic endurance training based on the physical fitness assessment results. The subjects will receive the CR training for 5 days and will be followed up for 6 months. The primary endpoints are the score of the short physical performance battery (SPPB) and 6-month all-cause rehospitalization. The secondary endpoints include cardio-pulmonary function, activities of daily living (ADL), in-hospital mortality rate and 6-month all-cause mortality rate.DiscussionThis randomized, controlled, clinical trial will assess whether CR improves physical function and reduces rehospitalization in patients hospitalized in CICU with ADHF. The results will provide further research-based evidence for the clinical application of CR in patients with ADHF.Trial RegistrationChinese Clinical Trial Registry ChiCTR2100050151. Registered on 19 August 2021.

3-D Ultrasonographic Quantification of Hand and Calf Muscle Volume: Statistical Shape Modeling Approach.

Accurate acquisition and segmentation of muscles are essential in 3-D freehand ultrasonography (US) to estimate in vivo muscle volume, but the source of segmentation inaccuracy in shape variation has never been the focus. This study was aimed at investigating reliability of 3-D US in the acquisition and segmentation for muscle volume of two muscles of different sizes and in identifying a primary source of measurement difference. The lateral gastrocnemius and flexor pollicis brevis of 12 healthy adults were assessed using freehand 3-D US scans. The motion-tracking data of the probe were synchronized with the B-mode ultrasound scan to reconstruct 3-D muscle volume. Statistical shape modeling was used to provide a spatial segmentation volume difference that further explains the variation around segmentation repeatability. The absolute difference of the flexor pollicis brevis was 3.5 percentage points greater than that for the lateral gastrocnemius. The highest measurement differences were observed when for inter-acquirer analysis. Statistical shape modeling revealed that the primary segmentation volume differences were at the muscle ends and edges, where the muscle interfaces with the surrounding muscles. Three-dimensional US is a reliable tool in the clinical setting, but care must be taken to ensure that acquisition and segmentation are consistent, particularly in a small muscle that interfaces with tendons and other soft tissues.

How northern elephant seals mobilise blubber for fuel when fasting

When food is scarce, most animals go into survival mode, reducing their activity to conserve energy. But not northern elephant seals (Mirounga angustirostris). Leaving their ocean feeding grounds and hauling themselves onto Californian and Mexican beaches for weeks, the females give birth, nursing their pups, while the males posture as they protect their harems; all of which they do while fasting. Jane Khudyakov from the University of the Pacific, USA, explains that during this time the animals depend on their extensive fat reserves for survival. However, it wasn't clear how the animals coordinate their tissue energy use while going without. ‘The cellular mechanisms that regulate these adaptations are still not fully understood’, she says. Teaming up with collaborators Dan Crocker (Sonoma State University, USA) and Dan Costa [University of California, Santa Cruz (UCSC), USA], Khudyakov and Rachel Holser (UCSC) headed down to the elephant seals’ breeding grounds at Año Nuevo State Reserve, USA, when the animals returned to moult, to find out.‘They shed old skin and hair within several weeks’, says Khudyakov, adding, ‘it literally peels off in sheets, which makes the beach very smelly’. However, the moulting females are easier to approach than when fasting in the breeding season while protecting their pups. Surrounded by the colony, Holser with colleagues from Costa's lab gently anaesthetised five animals that had just returned from 3–4 month foraging trips, ready for Khudyakov to take small blood, muscle and fat samples at the beginning and end of the moult. In addition, the team weighed the females, recording that the animals lost ∼3 kg per day – totalling ∼28% of their body mass over the ∼33 day period – in the form of skin, hair and fat.Back in the lab, Khudyakov and University of the Pacific undergraduates Serena Ly and Theron Niel extracted proteins from the muscle and blubber before Craig Vierra and Basma Hasan (University of the Pacific) joined them to analyse the protein content, alongside that of the blood sample. ‘We identified 1053 proteins in blubber, 711 in muscle and 260 in blood, most of which have not been studied before in seals’, says Khudyakov. Yet, when the team compared the composition of the muscle and blubber over the month-long fast, they found they had changed little. ‘This suggests that protein turnover in these tissues may be tightly controlled’, says Khudyakov. However, the quantities of three key proteins involved in fat accumulation reduced in all three tissues as the animals switched from storing to consuming fat.In contrast, 53 blood proteins involved in controlling and transporting lipids around the body increased dramatically, including hormones that regulate the release and transport of lipids and those that control how the body uses lipids as a fuel. ‘We think that changes in these proteins may help seals quickly switch their metabolism between feeding and fasting without any of the adverse effects that such rapid fat gain and loss would cause in humans’, says Khudyakov. And when the team checked on the quantities of fat circulating in the animals’ blood, they found that triglycerides – a form of fat – and high-density lipoproteins – ‘good’ cholesterol – did not change significantly, ‘suggesting that seals very tightly regulate their fat reserves, despite using them for energy, during fasting’, says Khudyakov.So, fasting elephant seals are able to sustain an active lifestyle by mobilising fats from their blubber in a controlled way. And Khudyakov is keen to find out how the proteins that regulate fat use change when the females produce full-fat (60%) milk for their pups, although that will require running the gauntlet of the fiercely protective mothers’ teeth.

Impact of Cell Seeding Density and Cell Confluence on Human Tissue Engineered Skeletal Muscle.

Tissue engineering methodologies have the potential to treat volumetric muscle loss via the growth of exogenous skeletal muscle grafts from small autogenous muscle biopsies. A significant obstacle preventing the widespread use of engineered skeletal muscle grafts in a clinical setting is the high number of skeletal muscle stem cells, known as satellite cells, required for fabrication of human-sized skeletal muscle tissue. Additionally, there is a lack of work adapting engineered constructs created for animal models into skeletal muscle engineered from a primary human skeletal muscle cell source. For this study, we used scaffold-free tissue-engineered skeletal muscle units (SMUs) to determine the impact of cell seeding density on the ability to fabricate functional human engineered skeletal muscle. Following established protocols, human skeletal muscle isolates were cultured into SMUs at five different cell seeding densities: 1000, 2500, 5000, 10,000, and 25,000 cells/cm2. Following previous human SMU work, SMUs prepared at a cell seeding density of 10,000 cells/cm2 served as controls. Additionally, the impact of cell monolayer confluency on the outcome of human cell-sourced SMU fabrication was investigated at both the 1000 and 10,000 cells/cm2 seeding densities. Light microscopy was used to examine myotube formation and hypertrophy in cell monolayers. After the formation of three-dimensional constructs, SMUs underwent maximum tetanic isometric force production measurements and immunohistochemical staining to examine SMU contractile function and muscle-like structure, respectively. Results indicate that the 25,000 cells/cm2 cell seeding density was detrimental to the contractile function of human cell-sourced SMUs, which had significantly lower maximum tetanic forces compared with SMUs seeded at lower densities. Compared with control, low cell seeding densities (1000-5000 cells/cm2) have no detrimental impact on SMU skeletal muscle growth, maturation, or contractility. Cell cultures seeded at 1000 cells/cm2 and allowed to proliferate to 90-100% confluency before treatment in muscle differentiation media (MDM) resulted in SMUs with greater contractile forces and total muscle structure compared with cell cultures switched to MDM when underconfluent or overconfluent. In conclusion, initial cell seeding density for SMU fabrication can be decreased to as low as 1000 cells/cm2 without negatively impacting SMU muscle-like structure and function. Impact Statement Our research suggests that during the translation of skeletal muscle tissue engineering technologies from animal to human cell sources, initial starting cell seeding density can be significantly lowered without negatively impacting engineered skeletal muscle growth, maturation, or contractile function. Decreasing the initial cell density, and, thus, the muscle biopsy size required to fabricate an engineered human skeletal muscle, increases the potential for the clinical adoption of tissue-engineered based therapies for volumetric muscle loss.

Magnolol and honokiol target TRPC4 to regulate extracellular calcium influx and relax intestinal smooth muscle

Ethnopharmacological relevanceMagnolia officinalis Cortex (M. officinalis) is a classical traditional Chinese medicine (TCM) widely used to treat digestive system diseases. It effectively regulates gastrointestinal motility to improve abdominal pain, abdominal distension and other symptoms. Magnolol (MAG) and honokiol (HON) are the main pharmacodynamic components responsible for the gastrointestinal activity of M. officinalis. Aim of the studyThe transient receptor potential (TRP) family is highly expressed in the gastrointestinal tract and participates in the regulation of gastrointestinal motility, visceral hypersensitivity, visceral secretion and other physiological activities. In this study, the calcium-lowering mechanisms of MAG and HON contributing to the smooth muscle relaxation associated with TRP are discussed. Materials and methodsThe relaxation smooth muscle effects of MAG and HON were tested by the isolated intestine tone tests. A synthetic MAG probe (MAG-P) was used to target fishing for their possible target. The distribution of MAG on the smooth muscle was identified by a molecular tracer based on chemical biology. Ca2+ imaging and dual-luciferase reporter assays were used to determine the effects on the target proteins. Finally, the calcium-mediating effects of MAG and HON on smooth muscle cells and TRPC4-knockdown cells were compared to verify the potential mechanism. ResultsAfter confirming the smooth muscle relaxation in the small intestine induced by MAG and HON, the relaxation effect was identified mainly due to the downregulation of intracellular calcium by controlling external calcium influx. Although MAG and HON inhibited both TRPV4 and TRPC4 channels to reduce calcium levels, the inhibitory effect on TRPC4 channels is an important mechanism of their smooth muscle relaxation effect, since TRPC4 is widely expressed in the small intestinal smooth muscle cells. ConclusionsThe inhibition of MAG and HON on TRPC4 channels contributes to the relaxation of intestinal smooth muscle.

Electromyographic and Systemic Physiological Thresholds in Single-Joint Elbow Flexion Movements.

Reported relationships between electromyographic (EMG) thresholds and systemic thresholds based on lactate, ventilation, or heart rate are contradictory. This might be related to the complexity of the investigated whole-body movements involving many muscles with different activation patterns. Therefore, the aim of the study was to investigate these relationships during an incremental single-joint exercise. Eighteen male subjects (29.7 [4.4]y) performed single-arm elbow flexions on a biceps curl machine with loads increasing every minute until exhaustion. EMG signals of the main elbow flexors (short and long head of the biceps brachii, flexor carpi radialis, and brachioradialis) as well as gas exchange variables, blood lactate concentration, and heart rate were measured, and 2 turn points based on a 3-phase model of metabolism were determined for each variable. The first and second turn points for EMG were determined at 32.0% to 33.1% and 64.4% to 66.5% of maximal achieved performance (maximum weight), respectively. Systemic turn points were determined at 33.3% to 34.4% and 65.9% to 66.7% of maximum weight and were not significantly different from EMG turn points. Furthermore, systemic and EMG turn points showed a strong or very strong relationship at the first (ρ = .54-.93, P < .05) and second turn point (ρ = .76-.93, P < .01). A close relationship between EMG and systemic turn points could be confirmed for the applied movement of a small muscle group. The determination of local single muscle thresholds using EMG provides additional muscle-specific information about performance-limiting properties of muscles involved in endurance-type incremental exercise.

Increased Mass-Specific Maximal Fat Oxidation Rate with Small versus Large Muscle Mass Exercise.

Skeletal muscle perfusion and oxygen (O2) delivery are restricted during whole-body exercise because of a limited cardiac output (Q˙). This study investigated the role of reducing central limitations to exercise on the maximal fat oxidation rate (MFO) by comparing mass-specific MFO (per kilogram of active lean mass) during one-legged (1L) and two-legged (2L) cycling. We hypothesized that the mass-specific MFO would be higher during 1L than 2L cycling. Twelve male subjects (V̇O2peak, 59.3 ± 8.4 mL·kg-1·min-1; mean ± SD) performed step-incremental 2L- (30%-80% of V̇O2peak) and 1L (50% of 2L power output, i.e., equal power output per leg) cycling (counterbalanced) while steady-state pulmonary gas exchanges, Q˙ (pulse-contour analysis), and skeletal muscle (vastus lateralis) oxygenation (near-infrared spectroscopy) were determined. MFO and the associated power output (FatMax) were calculated from pulmonary gas exchanges and stoichiometric equations. A counterweight (10.9 kg) was added to the contralateral pedal arm during 1L cycling. Leg lean mass was determined by DEXA. The absolute MFO was 24% lower (0.31 ± 0.12 vs 0.44 ± 0.20 g·min-1, P = 0.018), whereas mass-specific MFO was 52% higher (28 ± 11 vs 20 ± 10 mg·min-1·kg-1, P = 0.009) during 1L than 2L cycling. FatMax was similar expressed as power output per leg (60 ± 28 vs 58 ± 22 W, P = 0.649). Q˙ increased more from rest to exercise during 1L than 2L cycling when expressed per active leg (ANOVA main effect: P = 0.003). Tissue oxygenation index and Δ[deoxy(Hb + Mb)] were not different between exercise modes (ANOVA main effects: P ≥ 0.587), indicating similar skeletal muscle fractional O2 extraction. Mass-specific MFO is increased by exercising a small muscle mass, potentially explained by increased perfusion and more favorable conditions for O2 delivery than during whole-body exercise.