Changes In Electrophysiological Function Research Articles

Molecular autopsy and subsequent functional analysis reveal de novo DSG2 mutation as cause of sudden death

Sudden cardiac death (SCD) is a common cause of death in young adults. In up to 80% of cases a genetic cause is suspected. Next-generation sequencing of candidate genes can reveal the cause of SCD, provide prognostic management, and facilitate pre-symptomatic testing and prevention in relatives. Here we present a proband who experienced SCD in his sleep for which molecular autopsy was performed.We performed a post-mortem genetic analysis of a 49-year-old male who died during sleep after competitive kayaking, using a Cardiomyopathy and Primary Arrhythmia next-generation sequencing panel, each containing 51 candidate genes. Autopsy was not performed.Genetic testing of the proband resulted in missense variants in KCNQ1 (c.1449C > A; p.(Asn483Lys)) and DSG2 (c.2979G > T; p.(Gln993His)), both absent from the gnomAD database. Familial segregation analysis showed de novo occurrence of the DSG2 variant and presence of the KCNQ1 variant in the proband's mother and daughter. KCNQ1 p.(Asn483Lys) was predicted to be pathogenic by MutationTaster. However, none of the KCNQ1 variant carrying family members showed long QTc on ECG or Holter. We further functionally analysed this variant using patch-clamp in a heterologous expression system (Chinese Hamster Ovary (CHO) cells) expressing the KCNQ1 mutant in combination with KCNE1 wild type protein and showed no significant changes in electrophysiological function of Kv7.1.Based on the above evidence, we concluded that the DSG2 p.(Gln993His) variant is the most likely cause of SCD in the presented case, and that there is insufficient evidence that the identified KCNQ1 p.(Asn483Lys) variant would confer risk for SCD in his mother and daughter. Fortunately, the DSG2 variant was not inherited by the proband's two children. This case report indicates the added value of molecular autopsy and the importance of subsequent functional study of variants to inform patients and family members about the risk of variants they might carry.

SO065TYPE OF EXERCISE INTERVENTION AND MUSCLE FUNCTIONS IN CHRONIC HEMODIALYSIS PATIENTS

Abstract Background and Aims Decreased exercise capacity due to muscle weakness and exercise intolerance reduces the ability to perform activities of daily living in patients with end-stage kidney disease. Data on exercise type in dialysis population and its muscle effects are scarce. We aimed to determine the impact of training type (strength, resistance and mixed) on cardiovascular performance, muscle function (strength-speed parameters, electrophysiological function of muscles) in patients on hemodialysis maintenance. Method Eighty six dialysis patients underwent claster randomisation and were assigned to an exercise intervention groups: A - controlled endurance training during haemodialysis using rotors (MOTOmed letto2), B - controlled force training (resistance), C - Tai Chi training on non dialysis days. Intervention lasted 6 months, 3 times a week (A, B) and 2 times a week (C) for 60 minutes. The outcome measures were spiroergometry (VO2/VO2max), strength of the lower limbs and electromyographic examination. Values at the baseline and 6 months later were compared. Results 45 patients completed intervention period and were analysed. Mean age in group A was 64±12y (n-16), in B was 60,5±10y. (n-15) and in C – 68,5±9y. (n-14). Patients did not differ markedly between groups in term of sex, BMI, dialysis vintage and comorbidities. After 6 months of training, VO2 and VO2max increased significantly only in group B (resistance training) Δ12.7 % for VO2 and 12.9% for VO2max but not in A and C group (Fig.1.). Regarding force torque of quadriceps (ΔPT) in isometric conditions the highest peak values were measured in group B (resistance training), namely increase by 13.6% (p=0.0004) in right (R) and 14% (p<0.0001) in left (L); in group A (endurance) 3.2% in R and 3.7% in L; in group C (Tai Chi group) by 7% (p<0.05) in R and 6.8% (p<0.05) in L. In terms of changes in electrophysiological function of right (QEMG_R) and left (QEMG_L) quadriceps, there were increases: for group A by 10.5% (p<0.0001) and 9.6% (p<0.05); B 9.7% (p=0.0002) and 20.1% (p=0.0001); for C by 4.5% and 6.2% for R and L, respectively (Fig.2). In groups B and C significant increases in static force moments (Δ%PT) was associated with increases in electrophysiological action (Δ%QEMG), but in group A increase in EMG activity did not correspond with rise in muscle force (Fig.2). Conclusion Differences in muscle strength and functions were observed after 6 months of various type of exercise intervention in dialysis patients. Resistance training during dialysis showed the largest improvement in cardiorespiratory function and isometric leg muscle strength.

Large-effect mutations generate trade-off between predatory and locomotor ability during arms race coevolution with deadly prey.

Adaptive evolution in response to one selective challenge may disrupt other important aspects of performance. Such evolutionary trade‐offs are predicted to arise in the process of local adaptation, but it is unclear if these phenotypic compromises result from the antagonistic effects of simple amino acid substitutions. We tested for trade‐offs associated with beneficial mutations that confer tetrodotoxin (TTX) resistance in the voltage‐gated sodium channel (NaV1.4) in skeletal muscle of the common garter snake (Thamnophis sirtalis). Separate lineages in California and the Pacific Northwest independently evolved TTX‐resistant changes to the pore of NaV1.4 as a result of arms race coevolution with toxic prey, newts of the genus Taricha. Snakes from the California lineage that were homozygous for an allele known to confer large increases in toxin resistance (NaV1.4LVNV) had significantly reduced crawl speed compared to individuals with the ancestral TTX‐sensitive channel. Heterologous expression of native snake NaV1.4 proteins demonstrated that the same NaV1.4LVNV allele confers a dramatic increase in TTX resistance and a correlated decrease in overall channel excitability. Our results suggest the same mutations that accumulate during arms race coevolution and beneficially interfere with toxin‐binding also cause changes in electrophysiological function of the channel that may affect organismal performance. This trade‐off was only evident in the predator lineage where coevolution has led to the most extreme resistance phenotype, determined by four critical amino acid substitutions. If these biophysical changes also translate to a fitness cost—for example, through the inability of T. sirtalis to quickly escape predators—then pleiotropy at this single locus could contribute to observed variation in levels of TTX resistance across the mosaic landscape of coevolution.

Different Profile of mRNA Expression in Sinoatrial Node from Streptozotocin-Induced Diabetic Rat.

BackgroundExperiments in isolated perfused heart have shown that heart rate is lower and sinoatrial node (SAN) action potential duration is longer in streptozotocin (STZ)–induced diabetic rat compared to controls. In sino-atrial preparations the pacemaker cycle length and sino-atrial conduction time are prolonged in STZ heart. To further clarify the molecular basis of electrical disturbances in the diabetic heart the profile of mRNA encoding a wide variety of proteins associated with the generation and transmission of electrical activity has been evaluated in the SAN of STZ-induced diabetic rat heart.Methodology/Principal FindingsHeart rate was measured in isolated perfused heart with an extracellular suction electrode. Expression of mRNA encoding a variety of intercellular proteins, intracellular Ca2+-transport and regulatory proteins, cell membrane transport proteins and calcium, sodium and potassium channel proteins were measured in SAN and right atrial (RA) biopsies using real-time reverse transcription polymerase chain reaction techniques. Heart rate was lower in STZ (203±7 bpm) compared to control (239±11 bpm) rat. Among many differences in the profile of mRNA there are some worthy of particular emphasis. Expression of genes encoding some proteins were significantly downregulated in STZ-SAN: calcium channel, Cacng4 (7-fold); potassium channel, Kcnd2 whilst genes encoding some other proteins were significantly upregulated in STZ-SAN: gap junction, Gjc1; cell membrane transport, Slc8a1, Trpc1, Trpc6 (4-fold); intracellular Ca2+-transport, Ryr3; calcium channel Cacna1g, Cacna1h, Cacnb3; potassium channels, Kcnj5, Kcnk3 and natriuretic peptides, Nppa (5-fold) and Nppb (7-fold).Conclusions/SignificanceCollectively, this study has demonstrated differences in the profile of mRNA encoding a variety of proteins that are associated with the generation, conduction and regulation of electrical signals in the SAN of STZ-induced diabetic rat heart. Data from this study will provide a basis for a substantial range of future studies to investigate whether these changes in mRNA translate into changes in electrophysiological function.

Alterations in Hippocampal Network Activity after In Vitro Traumatic Brain Injury.

Traumatic brain injury (TBI) alters function and behavior, which can be characterized by changes in electrophysiological function in vitro. A common cognitive deficit after mild-to-moderate TBI is disruption of persistent working memory, of which the in vitro correlate is long-lasting, neuronal network synchronization that can be induced pharmacologically by the gamma-aminobutyric acid A antagonist, bicuculline. We utilized a novel in vitro platform for TBI research, the stretchable microelectrode array (SMEA), to investigate the effects of TBI on bicuculline-induced, long-lasting network synchronization in the hippocampus. Mechanical stimulation significantly disrupted bicuculline-induced, long-lasting network synchronization 24 h after injury, despite the continued ability of the injured neurons to fire, as revealed by a significant increase in the normalized spontaneous event rate in the dentate gyrus (DG) and CA1. A second challenge with bicuculline 24 h after the first challenge significantly decreased the normalized spontaneous event rate in the DG. In addition, we illustrate the utility of the SMEA for TBI research by combining multiple experimental paradigms in one platform, which has the potential to enable novel investigations into the mechanisms responsible for functional consequences of TBI and speed the rate of drug discovery.

Predicting changes in cortical electrophysiological function after in vitro traumatic brain injury.

Finite element (FE) models of traumatic brain injury (TBI) are capable of predicting injury-induced brain tissue deformation. However, current FE models are not equipped to predict the biological consequences of tissue deformation, which requires the determination of tolerance criteria relating the effects of mechanical stimuli to biologically relevant functional responses. To address this deficiency, we present functional tolerance criteria for the cortex for alterations in neuronal network electrophysiological function in response to controlled mechanical stimuli. Organotypic cortical slice cultures were mechanically injured via equibiaxial stretch with a well-characterized in vitro model of TBI at tissue strains and strain rates relevant to TBI (up to Lagrangian strain of 0.59 and strain rates up to 29 [Formula: see text]. At 4-6days post-injury, electrophysiological function was assessed simultaneously throughout the cortex using microelectrode arrays. Electrophysiological parameters associated with unstimulated spontaneous network activity (neural event rate, duration, and magnitude), stimulated evoked responses (the maximum response [Formula: see text], the stimulus current necessary for a half-maximal response [Formula: see text], and the electrophysiological parameter [Formula: see text] that is representative of firing uniformity), and evoked paired-pulse ratios at varying interstimulus intervals were quantified for each cortical slice culture. Nonlinear regression was performed between mechanical injury parameters as independent variables (tissue strain and strain rate) and each electrophysiological parameter as output. Parsimonious best-fit equations were determined from a large pool of candidate equations with tenfold cross-validation. Changes in electrophysiological parameters were dependent on strain and strain rate in a complex manner. Compared to the hippocampus, the cortex was less spontaneously active, less excitable, and less prone to significant changes in electrophysiological function in response to controlled deformation (strain or strain rate). Our study provides functional data that can be incorporated into FE models to improve their predictive capabilities of the in vivo consequences of TBI.

Hypertrophic phenotype in cardiac cell assemblies solely by structural cues and ensuing self‐organization

In vitro models of cardiac hypertrophy focus exclusively on applying "external" dynamic signals (electrical, mechanical, and chemical) to achieve a hypertrophic state. In contrast, here we set out to demonstrate the role of "self-organized" cellular architecture and activity in reprogramming cardiac cell/tissue function toward a hypertrophic phenotype. We report that in neonatal rat cardiomyocyte culture, subtle out-of-plane microtopographic cues alter cell attachment, increase biomechanical stresses, and induce not only structural remodeling, but also yield essential molecular and electrophysiological signatures of hypertrophy. Increased cell size and cell binucleation, molecular up-regulation of released atrial natriuretic peptide, altered expression of classic hypertrophy markers, ion channel remodeling, and corresponding changes in electrophysiological function indicate a state of hypertrophy on par with other in vitro and in vivo models. Clinically used antihypertrophic pharmacological treatments partially reversed hypertrophic behavior in this in vitro model. Partial least-squares regression analysis, combining gene expression and functional data, yielded clear separation of phenotypes (control: cells grown on flat surfaces; hypertrophic: cells grown on quasi-3-dimensional surfaces and treated). In summary, structural surface features can guide cardiac cell attachment, and the subsequent syncytial behavior can facilitate trophic signals, unexpectedly on par with externally applied mechanical, electrical, and chemical stimulation.

Atrial fibrillation in endurance-trained athletes

BackgroundEndurance exercise training produces multiple cardiac adaptations including changes in electrophysiological function that may make endurance-trained athletes more vulnerable to atrial fibrillation (AF). This possible association is not recognised by...

Energy requirements of glutamatergic pathways in rabbit retina

In vitro rabbit retina was used as an example of CNS tissue in experiments designed to measure the energy requirements associated with the activation of different types of glutamate receptors. Retinas were exposed to glutamate and to four analogs: kainate, 2-amino-4-phosphonobutyric acid (APB), 6-cyano-7-nitroquinoxaline-2,3-dione (CNQX), and 2-amino-5-phosphonovaleric acid (APV). The changes in O2 consumption and lactate production were determined using a recently developed experimental system that permitted simultaneous measurements of the rates at which O2 was removed from the medium and acid was added. The glutamatergic agents had relatively little effect on oxidative metabolism, but they caused large changes in glycolysis. Kainate increased retinal lactate production by 50%, whereas APB, CNQX, and APV reduced it by 23%, 19%, and 35%, respectively. Glutamate increased lactate production by 16% when administered after APB, but decreased it by 12% when administered after CNQX. The changes in energy metabolism coincided with changes in electrophysiological function. Since the energy metabolism of many retinal cells was presumably not much affected by the glutamatergic agents, the changes measured as a percent of total retinal glycolysis must have reflected considerably larger fractional changes in the cells most affected. From the response to inhibitors, it seems probable that even under resting conditions in darkness, activity in glutamatergic pathways is responsible for more than 50% of the glycolytically derived energy used by the cells involved. It also seems probable (particularly from the response to kainate) that under some circumstances the cells' energy metabolism and/or transport capability cannot meet the requirements imposed by glutamate-induced increases in function.(ABSTRACT TRUNCATED AT 250 WORDS)

The role of the perforant pathway as a trophic factor for neurotransmission in the rat dentate gyrus.

Changes in electrophysiological function in the hilar associational pathway terminating on dentate granule cells in the rat hippocampal formation were studied following unilateral entorhinal cortex lesions. In rats lesioned as pups (postnatal day 4 [PN 4]) or as adults (PN 60) there was a profound loss of paired-pulse inhibition at 30 days postlesion. Inhibition was unaffected at 10 days postlesion. Entorhinal cortex lesions did not affect population spike amplitude, population excitatory postsynaptic potentials slopes, or long-term potentiation compared to the unlesioned hemisphere. The presence of a complete hippocampal commissurotomy had no effect on excitatory or inhibitory parameters. Laminar analyses of extracellular field potentials from animals lesioned as adults revealed an expansion of functional synapses outward into the dentate molecular layer. This expansion was complete by 10 postlesion days. The changes observed with laminar analyses were not contemporaneous with the changes in paired-pulse inhibition. The loss of inhibition in the hilar associational pathway of entorhinal cortex-lesioned animals thus implies a change in local circuit function rather than an effect from sprouted associational fibers directly onto granule cells. The lack of inhibition in the associational pathway in lesioned animals was not due to a failure of local circuit inhibitory function to develop, since the same findings were obtained when lesions were made neonatally or as adults. Rather, the authors suggest that the present findings arise because of the formation of functional, recurrent, excitatory mossy fiber collateral synapses following entorhinal cortex lesions.