Reduction Of Contractile Activity Research Articles

Motor dysfunction of the gut in cystic fibrosis.

Cystic fibrosis (CF) is a multisystem disease caused by mutations in the cystic fibrosis transmembrane conductance regulator (CFTR) protein. Cystic fibrosis transmembrane conductance regulator is extensively expressed in the intestine and has an important role in the regulation of the viscosity and pH of gut secretions. Several studies have reported a delay in small bowel and colonic transit times in patients with CF which have been attributed to the secretory dysfunction. Our aim was to determine whether intestinal contractility is affected in these patients. Consecutive patients with CF referred to our institution between 2014 and 2017 (n=16) were prospectively investigated using automated non-invasive techniques for morpho-functional evaluation of the gut developed in our laboratory. On separate days, intraluminal images of the gut were obtained by capsule endoscopy and external images by abdominal MRI. Analysis of images (endoluminal and external) was performed with original, previously validated programs based on computer vision and machine learning techniques and compared with age- and sex-matched controls. Patients with CF exhibited important reduction in contractile activity and increased retention of static turbid luminal content in the small bowel by endoluminal image analysis. Morpho-volumetric analysis of MRI images found increased ileo-colonic volumes in CF. Significant correlations between abnormalities detected by intraluminal and external imaging techniques were found. The presence and severity of digestive symptoms were not related to abnormal gut function. Impaired transit and pooling of gut contents in patients with CF is associated with impaired intestinal motility.

Regulation of muscle mass: a new role for mitochondria?

The contribution of mitochondria to muscle adaptation to exercise is well known to all physiologists working on muscle plasticity and training. Since the classical paper by Holloszy (1967), a number of studies have demonstrated that endurance training can induce increases in mitochondrial density and in respiratory capacity of muscle fibres. More recently, the progress of knowledge in the field has delineated the signal chain based on AMPK and on PGC-1α and demonstrated the specific role of PGC-1α as the master gene able to activate mitochondrial biogenesis (see the recent review by Hawley et al. 2014). However, increasing amounts of evidence support the view that mitochondria are also involved in muscle mass regulation. The finding that PGC-1α overexpression protects against atrophy induced by denervation, fasting and other interventions through inhibition of FoxO gene expression (Sandri et al. 2006) was further corroborated by the observation that inhibition of mitochondrial fission has a similar protective or anti-atrophic effect (Romanello et al. 2010). This is in accordance with the view that the family of genes controlled by PGC-1α includes not only genes relevant for mitochondrial biogenesis but also genes which shift the balance between fission and fusion towards enhanced mitochondrial fusion. In muscle atrophy induced by denervation and fasting, the increased mitochondrial fission leads to a state of energy stress which activates AMPK and this in turn switches on FoxO3 and FoxO3-dependent transcription of atrogenes (Romanello et al. 2010). The question of whether such a mechanism could play a part in determining atrophy induced by disuse remains unanswered. In the present issue of The Journal of Physiology a paper by Cannavino and coworkers (2015) further strengthens the connection between mitochondrial impairment and muscle atrophy and gives an answer to the question concerning muscle atrophy in response to disuse. The paper represents the continuation of a previous study published by the same group (Cannavino et al. 2015). The model adopted in both studies was the ‘hindlimb suspension’ model in the mouse. The removal of load and the reduction of contractile activity can produce in a short time a very pronounced atrophy, in the order of 15% in less than one week. Starting from the widely accepted view that oxidative stress is a major cause of muscle degradation in disuse atrophy, the authors explored the response to an antioxidant treatment (administration of Trolox). Trolox was sufficient to control ROS accumulation and the specific antioxidant enzyme expression, but could not avoid the loss of muscle mass. In skeletal muscle fibres, ROS can derive from mitochondria as well as from other sources. The possible origin from mitochondrial metabolic impairment prompted the authors to analyse the mitochondrial metabolic function and mitochondrial dynamics. This analysis revealed that the mitochondria metabolic function was impaired and the balance between fission and fusion shifted towards fission. The demonstration of a causative connection between mitochondria and atrophy development was given by PGC-1α overexpression which at the same time prevented atrophy and restored the balance of the mitochondrial dynamics. It is worth emphasising the diversity among fast and slow muscles (see Fig. 1). In the slow soleus the primary event was the downregulation of PGC-1α followed by atrogene induction through FoxO3 disinhibition (Cannavino et al. 2015). In contrast, in the fast gastrocnemius the primary event was altered mitochondrial dynamics caused by downregulation of pro-fusion proteins and followed by energy stress and atrogene induction through AMPK activation. AMPK activation was sufficient to preserve PGC-1α expression (Cannavino et al. 2014). Importantly, in slow and fast muscles, the loss of mitochondria not only implies an impairment of aerobic metabolism, but also represents an ominous sign of imminent mass loss. Figure 1 Schematic representation of the different mechanisms leading to muscle atrophy in slow (soleus) and fast (gastrocnemius) muscles in the early phase of hindlimb suspension The results obtained by Cannavino and coworkers (2015 and 2014) are an important advance in our understanding of muscle adaptation to exercise and disuse and, additionally, represent a starting point for future work. New questions await an answer, such as, for example, the link between reduced loading and PGC-1α down-regulation or between reduced loading and mitochondria fission, the complex regulatory role played by AMPK and the definition of the retrograde signals that come from mitochondria and affect nuclear gene expression.

Opioid mediated activity and expression of mu and delta opioid receptors in isolated human term non-labouring myometrium

The existence of opioid receptors in mammalian myometrial tissue is now widely accepted. Previously enkephalin degrading enzymes have been shown to be elevated in pregnant rat uterus and a met-enkephalin analogue has been shown to alter spontaneous contractility of rat myometrium. Here we have undertaken studies to determine the effects of met-enkephalin on in vitro human myometrial contractility and investigate the expression of opioid receptors in pregnant myometrium. Myometrial biopsies were taken from women undergoing elective caesarean delivery at term. Organ bath experiments were used to investigate the effect of the met-enkephalin analogue [d-Ala 2, d-met 5] enkephalin (DAMEA) on spontaneous contractility. A confocal immunofluorescent technique and real time PCR were used to determine the expression of protein and mRNA, respectively for two opioid receptor subtypes, mu and delta. DAMEA had a concentration dependent inhibitory effect on contractile activity (1×10−7M–1×10−4M; 54% reduction in contractile activity, P<0.001 at 1×10−4M concentration). Mu and delta opioid receptor protein sub-types and their respective mRNA were identified in all tissues sampled. This is the first report of opioid receptor expression and of an opioid mediated uterorelaxant action in term human non-labouring myometrium in vitro.

Intestinal motor activity, endoluminal motion and transit

A programme for evaluation of intestinal motility has been recently developed based on endoluminal image analysis using computer vision methodology and machine learning techniques. Our aim was to determine the effect of intestinal muscle inhibition on wall motion, dynamics of luminal content and transit in the small bowel. Fourteen healthy subjects ingested the endoscopic capsule (Pillcam, Given Imaging) in fasting conditions. Seven of them received glucagon (4.8 microg kg(-1) bolus followed by a 9.6 microg kg(-1) h(-1) infusion during 1 h) and in the other seven, fasting activity was recorded, as controls. This dose of glucagon has previously shown to inhibit both tonic and phasic intestinal motor activity. Endoluminal image and displacement was analyzed by means of a computer vision programme specifically developed for the evaluation of muscular activity (contractile and non-contractile patterns), intestinal contents, endoluminal motion and transit. Thirty-minute periods before, during and after glucagon infusion were analyzed and compared with equivalent periods in controls. No differences were found in the parameters measured during the baseline (pretest) periods when comparing glucagon and control experiments. During glucagon infusion, there was a significant reduction in contractile activity (0.2 +/- 0.1 vs 4.2 +/- 0.9 luminal closures per min, P < 0.05; 0.4 +/- 0.1 vs 3.4 +/- 1.2% of images with radial wrinkles, P < 0.05) and a significant reduction of endoluminal motion (82 +/- 9 vs 21 +/- 10% of static images, P < 0.05). Endoluminal image analysis, by means of computer vision and machine learning techniques, can reliably detect reduced intestinal muscle activity and motion.

Increased relaxant action of forskolin and isoproterenol against muscarinic agonist-induced contractions in smooth muscle from M2 receptor knockout mice.

The ability of forskolin and isoproterenol to inhibit the contractile action of the muscarinic agonist, oxotremorine-M, was investigated in smooth muscle from wild-type and M(2) muscarinic receptor knockout mice. Forskolin (5.0 micro M) caused a significant reduction in the contractile activity of oxotremorine-M in ileum, trachea, and urinary bladder from both wild-type and M(2) muscarinic receptor knockout mice. This reduction in contractile activity was characterized by decreases in potency or maximal response, but not always both. Similar results were obtained with isoproterenol (1.0 micro M). The relaxant effects of forskolin in ileum, trachea, and urinary bladder from M(2) receptor knockout mice were approximately 3- to 9-fold greater than those observed in the same tissues from wild-type mice. Similar results were obtained with isoproterenol in ileum and urinary bladder, although the differences between wild-type and M(2) receptor knockout tissues were less than those observed with forskolin. In contrast, there was no significant difference between the relaxant effect of isoproterenol in trachea from wild-type and M(2) receptor knockout mice. In contrast to the results observed with oxotremorine-M as the contractile agent, forskolin and isoproterenol did not exhibit greater relaxant activity against KCl-induced contractions in M(2) receptor knockout mice compared with wild-type mice. These results suggest that a component of the contractile response to muscarinic agonists in smooth muscle involves an M(2) muscarinic receptor-mediated inhibition of the relaxant effects of agents that increase cAMP levels.

In vitro investigation of the effects of cyclooxygenase-2 inhibitors on contractile activity of the equine dorsal and ventral colon.

To evaluate the effect of 2 cyclooxygenase (COX)-2 inhibitors on contractile activity of the circular smooth muscle layer of the equine dorsal and ventral colon. Samples of the dorsal and ventral colon obtained from 10 healthy horses. Full-thickness tissue samples were collected from the dorsal colon in the area of the diaphragmatic flexure and the ventral colon in the area of the sternal flexure. Samples were cut into strips oriented along the fibers of the circular muscle layer and mounted in a tissue bath system for determination of contractile strength. Incremental amounts of etodolac, nabumetone, and indomethacin were added, and contractile activity was recorded. Response of the dorsal and ventral colon to nonsteroidal anti-inflammatory drugs (NSAIDs) was variable. Indomethacin induced the greatest reduction in contractile activity, followed by nabumetone. For etodolac, the difference from baseline values was only significantly reduced at the highest concentration used (1 X 10(5)M) for the ventral colon. The NSAIDs that are designed to target the COX-2 isoform appeared to have variable effects on the contractile activity of the equine dorsal and ventral colon. Etodolac appeared to have the least effect on contractile activity, compared with the effects attributable to nabumetone, and would potentially have the fewest adverse effects relative to motility of the dorsal and ventral colon.

Exercise inhibits glucocorticoid-induced glutamine synthetase expression in red skeletal muscles.

One purpose of this study was to determine whether the suppression of glucocorticoid-induced glutamine synthetase (GS) gene expression by exercise is localized to fiber types that are known to be primarily recruited during endurance running. A second purpose examined whether denervation, which is associated with a reduction in contractile activity, would upregulate GS expression. Exercise consisted of treadmill running at 31 m/min for 12-16 wk. Glucocorticoid treatment (100 mg/kg body wt hydrocortisone 21-acetate) was administered during the last 11 days of the exercise program. Basal GS expression was lowest (GS enzyme activity, 43 +/- 3 nmol.h-1.mg protein-1; GS mRNA, 1.0 arbitrary units) in the slow-twitch red soleus, a muscle type that is known to resist glucocorticoid-induced muscle wasting, intermediate (74 +/- 10 and 1.7 +/- 0.2) in fast-twitch red quadriceps, a muscle type susceptible to atrophy, and highest (106 +/- 16 and 5.4 +/- 1.3) in fast-twitch white quadriceps, a muscle type known to be most susceptible to atrophy. Hormone treatment increased GS enzyme activity and mRNA by two- to fourfold in all muscle types. Exercise diminished GS enzyme activity and mRNA in the fast-twitch red fibers to 35-70% of sedentary control values in both basal and glucocorticoid-stimulated muscles. The running also reduced GS enzyme activity in hormone-treated slow-twitch fibers but did not alter basal or glucocorticoid-induced GS expression in fast-twitch white fibers. These results indicate that glucocorticoids induce similar relative GS expression across all muscle types, but the low absolute levels of expression in slow-twitch muscles are not related to any atrophy.(ABSTRACT TRUNCATED AT 250 WORDS)

Effect of felodipine on the myogenic response to dynamic stretch in vascular smooth muscle

In the present experiments we examined the effect of felodipine, a vasoselective dihydropyridine calcium antagonist, on contractile responses to dynamic and static stretch of the isolated portal vein of the rat. Dynamic stretch was applied to the vascular smooth muscle at graded rates (from 0.5-1.5% muscle length s-1). Earlier observations (Johansson & Mellander 1975) of a rate-dependent excitation of the vascular smooth muscle by dynamic stretch were confirmed. Addition of felodipine, 3 nM, reduced the spontaneous activity at static lengths to about 50% but resulted in much stronger inhibition of the dynamic stretch responses. Particularly the rate-dependent increase in active force was no longer evident since the response at high rates of passive lengthening was most clearly reduced by felodipine. By contrast, lowering of the extracellular Ca2+ concentration resulted in a comparable attenuation of the spontaneous contractile activity and of the dynamic stretch responses which still showed the typical rate dependence. Therefore, the pronounced inhibition by felodipine of the dynamic myogenic reactivity of the rat portal vein appeared to be a specific effect and not simply related to the overall reduction in contractile activity. We suggest that felodipine, in addition to its inhibition of action potentials and excitation-contraction coupling may exert a special negative influence on the mechano-electrical coupling, i.e. the process that couples dynamic stretch of the vascular smooth muscle to membrane excitation.

Inhibitory innervation of colonic smooth muscle cells and interstitial cells of Cajal

The effect of neural inhibition on the electrical activities of circular and longitudinal colonic smooth muscle was investigated. In addition, a comparative study was carried out between circular muscle preparations with and without the "submucosal" and "myenteric plexus" network of interstitial cells of Cajal (ICC) to study innervation of the "submucosal" ICC and to investigate whether or not the ICC network is an essential intermediary system for inhibitory innervation of smooth muscle cells. Electrical stimulation of intrinsic nerves in the presence of atropine caused inhibitory junction potentials (ijps) throughout the circular and longitudinal muscle layers. The ijp amplitude depended on the membrane potential and not on the location of the muscle cells with respect to the ICC network. Neurally mediated inhibition of the colon resulted in a reduction in amplitude and duration of slow wave type action potentials in circular and abolishment of spike-like action potentials in longitudinal smooth muscle, both resulting in a reduction of contractile activity. With respect to mediation by ICC, the study shows (i) "submucosal" ICC receive direct inhibitory innervation and (ii) circular smooth muscle cells can be directly innervated by inhibitory nerves without ICC as necessary intermediaries. The reversal potential of the ijp in colonic smooth muscle was observed to be approximately -76 mV, close to the estimated potassium equilibrium potential, suggesting that the nerve-mediated hyperpolarization is caused by increased potassium conductance.

Differential inhibition of regional gastrointestinal tissue to progesterone in the rat

The influence of progesterone on contractile activity of three gastrointestinal regional tissues was evaluated. Up to six dose levels of progesterone were administered subcutaneously to male rats daily for four days. Progesterone blood levels measured with radioimmunoassay on the fourth day revealed that the range of progesterone exposure to the male animals did not exceed the progesterone blood level peak reported during the normal hormonal cycle of female rats. Log-dose response curves indicate that esophageal, antral, and colonic tissues from progesterone treated animals showed a significant reduction in contractile activity compared to the corresponding tissue from non-progesterone treated control animals. Esophageal and colonic tissues were two and 12-fold, respectively, more sensitive to the inhibitory progesterone influence compared to antral tissue. This study supports the concept that normal circulating levels of progesterone may have an influence on specific gastrointestinal regional function in addition to the effects of progesterone blood levels during pregnancy.

Role of Prostaglandin Production in Spontaneous and Oxytocin-Induced Uterine Contractile Activity in in Vitro Pregnant Rat Uteri*

The role of prostaglandins (PGs) in spontaneous and oxytocin-induced uterine contractions was studied. Uterine segments from pregnant rats were monitored in vitro for isometric contractile activity in Krebs-Ringer medium (95% O2-5% CO2; 37 C). The medium was sampled periodically and assayed for PGE, PGF, and, in some cases, 13,14-dihydro-15-keto-PGF2a, by RIA. Uteri from 21-day pregnant rats demonstrated more PGE and PGF release and greater integrated contractile force (ICF) than uteri from 18-day pregnant rats. Upon analysis of the more active uteri of 21-day pregnant rats, a significant positive correlation was found between PG production and either ICF (P < 0.05) or contractile frequency (P < 0.001) but not with amplitude or duration of contractions. Oxytocin (20 mU) caused increased contractile activity in 18-day pregnant rat uteri, but no increase in PGE, PGF, or 13,14-dihydro-15-keto-PGF2a was observed. Indomethacin caused a decrease in PG proction as well as a reduction in contractile activity. Ind...