Long-lasting muscle fatigue: partial disruption of excitation-contraction coupling by elevated cytosolic Ca2+ concentration during contractions

2006 ◽  
Vol 290 (4) ◽  
pp. C1199-C1208 ◽  
Author(s):  
Esther Verburg ◽  
Travis L. Dutka ◽  
Graham D. Lamb

The repeated elevation of cytosolic Ca2+ concentration ([Ca2+]i) above resting levels during contractile activity has been associated with long-lasting muscle fatigue. The mechanism underlying this fatigue appears to involve elevated [Ca2+]i levels that induce disruption of the excitation-contraction (E-C) coupling process at the triad junction. Unclear, however, are which aspects of the activity-related [Ca2+]i changes are responsible for the deleterious effects, in particular whether they depend primarily on the peak [Ca2+]i reached locally at particular sites or on the temporal summation of the increased [Ca2+] in the cytoplasm as a whole. In this study, we used mechanically skinned fibers from rat extensor digitorum longus muscle, in which the normal E-C coupling process remains intact. The [Ca2+]i was raised either by applying a set elevated [Ca2+] throughout the fiber or by using action potential stimulation to induce the release of sarcoplasmic reticulum Ca2+ by the normal E-C coupling system with or without augmentation by caffeine or buffering with BAPTA. Herein we show that elevating [Ca2+]i in the physiological range of 2–20 μM irreversibly disrupts E-C coupling in a concentration-dependent manner but requires exposure for a relatively long time (1–3 min) to cause substantial uncoupling. The effectiveness of Ca2+ released via the endogenous system in disrupting E-C coupling indicates that the relatively high [Ca2+]i attained close to the release site at the triad junction is a more important factor than the increase in bulk [Ca2+]i. Our results suggest that during prolonged vigorous activity, the many repeated episodes of relatively high triadic [Ca2+] can disrupt E-C coupling and lead to long-lasting fatigue.

Biomolecules ◽  
2020 ◽  
Vol 10 (10) ◽  
pp. 1440
Author(s):  
Monique Rascher ◽  
Kathrin Wittstein ◽  
Barbara Winter ◽  
Zeljka Rupcic ◽  
Alexandra Wolf-Asseburg ◽  
...  

Medicinal mushrooms of the genus Hericium are known to produce secondary metabolites with homeostatic properties for the central nervous system. We and others have recently demonstrated that among these metabolites cyathane diterpenoids and in particular erinacine C possess potent neurotrophin inducing properties in astrocytic cells. Yet, the signaling events downstream of erinacine C induced neurotrophin acitivity in neural-like adrenal phaeochromocytoma cells (PC12) cells have remained elusive. Similar, signaling events activated by erinacine C in astrocytic cells are unknown. Using a combination of genetic and pharmacological inhibitors we show that erinacine C induced neurotrophic activity mediates PC12 cell differentiation via the TrkA receptor and likely its associated PLCγ-, PI3K-, and MAPK/ERK pathways. Furthermore, a small library of transcriptional activation reporters revealed that erinacine C induces transcriptional activation mediated by DNA consensus binding sites of selected conserved transcription factor families. Among these, transcription is activated from an ETS consensus in a concentration dependent manner. Interestingly, induced ETS-consensus transcription occurs in parallel and independent of neurotrophin induction. This finding helps to explain the many pleiotropic functions of cyathane diterpenoids. Moreover, our studies provide genetic access to cyathane diterpenoid functions in astrocytic cells and help to mechanistically understand the action of cyathanes in glial cells.


1993 ◽  
Vol 70 (2) ◽  
pp. 758-764 ◽  
Author(s):  
E. Garcia ◽  
A. Benitez ◽  
C. G. Onetti

1. An electrophysiological study of the D-glucose sensitivity of X-organ (XO) neurosecretory cell bodies in crayfish was carried out with the use of microelectrodes, perforated, and cell-attached patch-clamp techniques. 2. Glucose depolarizes the membrane potential of XO cells in a concentration-dependent manner. 3. Depolarization produced by glucose initiates a change in the pattern of electrical activity. Silent cells began to discharge action potentials. When bursting cells are depolarized by glucose, their action potentials are no longer grouped in bursts or disappear entirely. 4. Although the membrane potential returns to its initial value after removing glucose from the bath, discharge patterns of the cells may remain different. This suggests that besides the depolarizing effect, once the cells have been exposed to glucose, the sugar switches on a process that is maintained for a long time. 5. Glucose produced a reduction of membrane steady-state conductance, and a shift of reversal potential of membrane currents to a more positive value. 6. Depolarization induced by D-glucose appears to be related with a closure of potassium channels. 7. Glucose effect was thought to be generated by a product of metabolism that would act as intracellular mediator.


2010 ◽  
Vol 88 (8) ◽  
pp. 840-849 ◽  
Author(s):  
Faquan Liang ◽  
Christopher B. Glascock ◽  
Denise L. Schafer ◽  
Jennifer Sandoval ◽  
LouAnn Cable ◽  
...  

Endothelin is a potent vasoconstrictor often up-regulated in hypertension. Endothelin vasoconstriction is mediated via the G-protein coupled endothelin A (ETA) receptor present on vascular smooth muscle. Endothelin receptor antagonists (ERAs) have been shown to antagonize ET-induced vasoconstriction. We describe the primary pharmacology of darusentan, a propanoic acid based ERA currently in phase 3 clinical trials for resistant hypertension. Darusentan was tested in membrane-, cell-, and tissue-based assays to determine its biochemical and functional potency. Rat aortic vascular smooth muscle cells (RAVSMs) were characterized using flow cytometry. RAVSM membrane fractions tested in saturation experiments exhibited moderate endothelin receptor density. Receptor counting revealed that >95% of the endothelin receptors in these fractions were the ETA subtype. (S)-Darusentan competed for radiolabeled endothelin binding in RAVSM membranes with single-site kinetics, exhibiting a Ki = 13 nmol/L. (R)-Darusentan exhibited no binding activity. In cultured RAVSMs, endothelin induced increases in inositol phosphate and Ca2+ signaling, both of which were attenuated by (S)-darusentan in a concentration-dependent manner. In isolated endothelium-denuded rat aortic rings, (S)-darusentan inhibited endothelin-induced vascular contractility with a pA2 = 8.1 ± 0.14 (n = 4 animals; mean ± SD). (R)-Darusentan had no effect. The vasorelaxant potency of (S)-darusentan did not change when determined in isolated denuded rat mesenteric arterioles, suggesting a similar mode of action in both conductance and resistance arteries. In vascular smooth muscle, (S)-darusentan is an ERA with high affinity for the ET receptor, which in this preparation is predominantly ETA receptors. (S)-Darusentan inhibits endothelin-induced signaling related to pro-contractile activity and is a potent inhibitor of vasoconstriction in large and small arteries.


2015 ◽  
Vol 10 (4) ◽  
pp. 1934578X1501000 ◽  
Author(s):  
Natalia Prissadova ◽  
Petko Bozov ◽  
Kiril Marinkov ◽  
Hristo Badakov ◽  
Atanas Kristev

Ursolic acid (UA) in concentrations of 1×10−7 mol/L - 5×10−5 mol/L induced relaxation in gastric smooth muscle (SM) tissues, in a concentration-dependent manner. The relaxation did not change membrane potential and slow wave contraction patterns. A significant decrease in amplitude and frequency of spike-potentials was observed. UA-induced reactivity was removed when SM preparations were treated with nifedipine (1×10−6 mol/L). Ca2+- induced contractions of the depolarized SM preparations (42 mmol/L K+; Ca2+- free Krebs solution) were substantially reduced in the presence of UA. It was determined that, in certain concentrations, UA influenced L – type Ca2+ channels, and reduced the Ca2+ influx.


2001 ◽  
Vol 79 (7) ◽  
pp. 580-584 ◽  
Author(s):  
Pal Pacher ◽  
Zoltan Ungvari ◽  
Valéria Kecskeméti ◽  
Tamás Friedmann ◽  
Susanna Furst

Selective serotonin reuptake inhibitor antidepressants (SSRIs) exert depressant effects on cardiac myocytes and vascular smooth muscle cells by inhibiting Ca2+ channels. We hypothesized that the SSRIs fluoxetine and citalopram affect the contractile activity of intestinal smooth muscle by interfering with Ca2+ entry and (or) signaling pathways. The effects of fluoxetine and citalopram on contractions of guinea-pig ileum longitudinal muscle-myenteric plexus preparations (LMMP) were compared with the effects of the voltage-operated Ca2+ channel inhibitors nifedipine and diltiazem. In a concentration-dependent manner, nifedipine, diltiazem, fluoxetine, and citalopram elicited relaxation of LMMPs contracted by electrical field stimulation (EC50 values of 4 × 10–7 M, 1.4 × 10–6 M, 1.4 × 10–5, and 6.8 × 10–6 M, respectively). Nifedipine, diltiazem, fluoxetine, and citalopram also relaxed LMMPs contracted with a depolarizing concentration of KCl (48 mM; EC50 values of 1.8 × 10–8 M, 1.4 × 10–7 M, 3.7 × 10–6 M, and 6.3 × 10–6, respectively), a response that could be reversed by increasing the extracellular Ca2+ concentration (2.5–30 mM). These data suggest that fluoxetine and citalopram elicit relaxation of intestinal smooth muscle, likely by inhibiting Ca2+ channel(s). This effect may be of clinical importance.Key words: fluoxetine (Prozac(r)), citalopram (Seropram(r)), nifedipine, diltiazem, L-type Ca2+ channels, intestinal smooth muscle.


1994 ◽  
Vol 266 (4) ◽  
pp. L414-L425 ◽  
Author(s):  
A. Abela ◽  
E. E. Daniel

The leukotrienes (LTs), referred to as the slow-reacting substance of anaphylaxis (SRS-A), are reported to have little or no activity in the canine airway. The objective of this study was to determine whether LTC4, LTD4, and LTE4 (10(-10)-10(-7) M) play a role in neuromuscular control of third- to fifth-order canine bronchi. In the presence of 1 microM indomethacin (Indo), canine bronchial smooth muscle contracted and was depolarized in a concentration-dependent manner by LTC4 or LTD4 but not by LTE4. LTC4 and LTD4 concentration-response curves were not significantly affected when conducted in the presence of any of the following: 10(-7) M propranolol (beta-adrenoceptor antagonist), 10(-6) M chlorpheniramine (H1-receptor antagonist), 10(-6) M ketanserin (nonselective 5-hydroxytryptamine receptor antagonist), 10(-7) M atropine (muscarinic receptor antagonist), and 10(-6) M tetrodotoxin (sodium channel blocker). LTC4 and LTD4 also potentiated electrical field-stimulated (EFS) excitatory junction potentials (EJPs), suggesting a possible prejunctional enhancement of acetylcholine release. In the absence of Indo, no postjunctional responses to LTC4 and LTD4 occurred. Endogenous prostaglandin E2 (PGE2) and 6-keto-PGF1 alpha (a stable metabolite of PGI2) levels from canine bronchi were significantly reduced by Indo. In the presence of Indo, addition of > or = 10(-8) M of PGE2 suppressed contractions to LTC4 and LTD4. These data suggest that the decrease in PGE2 and PGI2 production by Indo is sufficient to unmask the excitatory postjunctional actions of LTC4 and LTD4 on bronchial smooth muscle. Serine borate (45 mM; an inhibitor of gamma-glutamyl transpeptidase, which prevents the conversion of LTC4 to LTD4) increased selectively the contractile activity of LTC4. L-Cysteine (3 mM; an inhibitor of an aminopeptidase, which prevents the conversion of LTD4 to LTE4) enhanced the contractile responses to LTD4. Serine borate increased the amplitude and duration of EFS contractions and potentiated the amplitude of EFS EJPs; the last effects were prevented by nordihydroguaiaretic acid. These and other studies suggest that LTs are synthesized by canine bronchi and have receptors on canine bronchial smooth muscle but that contractions to LTC4 and LTD4 in the canine airway are usually not observed because of the presence of inhibitory prostanoids (PGE2 and PGI2). We suggest that decreases in PGE2 and PGI2 in models of airway disease in combination with increases in LTC4, LTD4, and thromboxane A2 may contribute to airway hyperresponsiveness in vitro.


2005 ◽  
Vol 288 (4) ◽  
pp. C824-C830 ◽  
Author(s):  
John N. Dentel ◽  
Samuel G. Blanchard ◽  
David P. Ankrapp ◽  
Laura R. McCabe ◽  
Robert W. Wiseman

Mitogen-activated protein kinases (MAPKs), in particular p38 MAPK, are phosphorylated in response to contractile activity, yet the mechanism for this is not understood. We tested the hypothesis that the force of contraction is responsible for p38 MAPK phosphorylation in skeletal muscle. Extensor digitorum longus (EDL) muscles isolated from adult male Swiss Webster mice were stimulated at fixed length at 10 Hz for 15 min and then subjected to Western blot analysis for the phosphorylation of p38 MAPK and ERK1/2. Contralateral muscles were fixed at resting length and were not stimulated. Stimulated muscles showed a 2.5-fold increase in phosphorylated p38 MAPK relative to nonstimulated contralateral controls, and there was no change in the phosphorylation of ERK1/2. When contractile activity was inhibited with N-benzyl- p-toluene sulfonamide (BTS), a specific inhibitor of actomyosin ATPase, force production decreased in both a time- and concentration-dependent manner. Preincubation with 25, 75, and 150 μM BTS caused 78 ± 4%, 97 ± 0.2%, and 99 ± 0.2% inhibition in contractile force, respectively, and was stable after 30 min of treatment. Fluorescence measurements demonstrated that Ca2+ cycling was minimally affected by BTS treatment. Surprisingly, BTS did not suppress the level of p38 MAPK phosphorylation in stimulated muscles. These data do not support the view that force generation per se activates p38 MAPK and suggest that other events associated with contraction must be responsible.


2014 ◽  
Vol 84 (1-2) ◽  
pp. 79-91 ◽  
Author(s):  
Amin F. Majdalawieh ◽  
Hyo-Sung Ro

Background: Foam cell formation resulting from disrupted macrophage cholesterol efflux, which is triggered by PPARγ1 and LXRα, is a hallmark of atherosclerosis. Sesamin and sesame oil exert anti-atherogenic effects in vivo. However, the exact molecular mechanisms underlying such effects are not fully understood. Aim: This study examines the potential effects of sesamin (0, 25, 50, 75, 100 μM) on PPARγ1 and LXRα expression and transcriptional activity as well as macrophage cholesterol efflux. Methods: PPARγ1 and LXRα expression and transcriptional activity are assessed by luciferase reporter assays. Macrophage cholesterol efflux is evaluated by ApoAI-specific cholesterol efflux assays. Results: The 50 μM, 75 μM, and 100 μM concentrations of sesamin up-regulated the expression of PPARγ1 (p< 0.001, p < 0.001, p < 0.001, respectively) and LXRα (p = 0.002, p < 0.001, p < 0.001, respectively) in a concentration-dependent manner. Moreover, 75 μM and 100 μM concentrations of sesamin led to 5.2-fold (p < 0.001) and 6.0-fold (p<0.001) increases in PPAR transcriptional activity and 3.9-fold (p< 0.001) and 4.2-fold (p < 0.001) increases in LXR transcriptional activity, respectively, in a concentration- and time-dependent manner via MAPK signaling. Consistently, 50 μM, 75 μM, and 100 μM concentrations of sesamin improved macrophage cholesterol efflux by 2.7-fold (p < 0.001), 4.2-fold (p < 0.001), and 4.2-fold (p < 0.001), respectively, via MAPK signaling. Conclusion: Our findings shed light on the molecular mechanism(s) underlying sesamin’s anti-atherogenic effects, which seem to be due, at least in part, to its ability to up-regulate PPARγ1 and LXRα expression and transcriptional activity, improving macrophage cholesterol efflux. We anticipate that sesamin may be used as a therapeutic agent for treating atherosclerosis.


1992 ◽  
Vol 68 (05) ◽  
pp. 570-576 ◽  
Author(s):  
Mary A Selak

SummaryWe have previously demonstrated that human neutrophil cathepsin G is a strong platelet agonist that binds to a specific receptor. This work describes the effect of neutrophil elastase on cathepsin G-induced platelet responses. While platelets were not activated by high concentrations of neutrophil elastase by itself, elastase enhanced aggregation, secretion and calcium mobilization induced by low concentrations of cathepsin G. Platelet aggregation and secretion were potentiated in a concentration-dependent manner by neutrophil elastase with maximal responses observable at 200 nM. Enhancement was observed when elastase was preincubated with platelets for time intervals of 10–60 s prior to addition of a low concentration of cathepsin G and required catalytically-active elastase since phenylmethanesulphonyl fluoride-inhibited enzyme failed to potentiate cell activation. Neutrophil elastase potentiation of platelet responses induced by low concentrations of cathepsin G was markedly inhibited by creatine phosphate/creatine phosphokinase and/or indomethacin, indicating that the synergism between elastase and cathepsin G required the participation of ADP and thromboxane A2. On the other hand, platelet responses were not attenuated by the PAF antagonist BN 52021, signifying that PAF-acether did not play a role in elastase potentiation. At higher concentrations porcine pancreatic elastase exhibits similar effects to neutrophil elastase, demonstrating that the effect of elastase was not unique to the neutrophil protease. While neutrophil elastase failed to alter the ability of cathepsin G to hydrolyze a synthetic chromogenic substrate, preincubation of platelets with elastase increased the apparent affinity of cathepsin G binding to platelets. In contrast to their effect on cathepsin G-induced platelet responses, neither neutrophil nor pancreatic elasatse potentiated aggregation or dense granule release initiated by ADP, PAF-acether, arachidonic acid or U46619, a thromboxane A2 mimetic. Moreover, unlike its effect on cathepsin G, neutrophil elastase inhibited thrombin-induced responses. The current observations demonstrate that elastase can potentiate platelet responses mediated by low concentrations of cathepsin G, suggesting that both enzymes may function synergistically to activate platelets under conditions where neutrophil degranulation occurs.


1993 ◽  
Vol 69 (03) ◽  
pp. 286-292 ◽  
Author(s):  
Che-Ming Teng ◽  
Feng-Nien Ko ◽  
Inn-Ho Tsai ◽  
Man-Ling Hung ◽  
Tur-Fu Huang

SummaryTrimucytin is a potent platelet aggregation inducer isolated from Trimeresurus mucrosquamatus snake venom. Similar to collagen, trimucytin has a run of (Gly-Pro-X) repeats at the N-terminal amino acids sequence. It induced platelet aggregation, ATP release and thromboxane formation in rabbit platelets in a concentration-dependent manner. The aggregation was not due to released ADP since it was not suppressed by creatine phosphate/creatine phosphokinase. It was not either due to thromboxane A2 formation because indomethacin and BW755C did not have any effect on the aggregation even thromboxane B2 formation was completely abolished by indomethacin. Platelet-activating factor (PAF) was not involved in the aggregation since a PAF antagonist, kadsurenone, did not affect. However, RGD-containing peptide triflavin inhibited the aggregation, but not the release of ATP, of platelets induced by trimucytin. Indomethacin, mepacrine, prostaglandin E1 and tetracaine inhibited the thromboxane B2 formation of platelets caused by collagen and trimucytin. Forskolin and sodium nitroprusside inhibited both platelet aggregation and ATP release, but not the shape change induced by trimucytin. In quin-2 loaded platelets, the rise of intracellular calcium concentration caused by trimucytin was decreased by 12-O-tetradecanoyl phorbol-13 acetate, imipramine, TMB-8 and indomethacin. In the absence of extracellular calcium, both collagen and trimucytin caused no thromboxane B2 formation, but still induced ATP release which was completely blocked by R 59022. Inositol phosphate formation in platelets was markedly enhanced by trimucytin and collagen. MAB1988, an antibody against platelet membrane glycoprotein Ia, inhibited trimucytinand collagen-induced platelet aggregation and ATP release. However, trimucytin did not replace the binding of 125I-labeled MAB1988 to platelets. Platelets pre-exposed to trimucytin were resistant to the second challenge with trimucytin itself or collagen. It is concluded that trimucytin may activate collagen receptors on platelet membrane, and cause aggregation and release mainly through phospholipase C-phosphoinositide pathway.


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