1
|
Bolaños P, Calderón JC. Excitation-contraction coupling in mammalian skeletal muscle: Blending old and last-decade research. Front Physiol 2022; 13:989796. [PMID: 36117698 PMCID: PMC9478590 DOI: 10.3389/fphys.2022.989796] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/08/2022] [Accepted: 08/08/2022] [Indexed: 11/13/2022] Open
Abstract
The excitation–contraction coupling (ECC) in skeletal muscle refers to the Ca2+-mediated link between the membrane excitation and the mechanical contraction. The initiation and propagation of an action potential through the membranous system of the sarcolemma and the tubular network lead to the activation of the Ca2+-release units (CRU): tightly coupled dihydropyridine and ryanodine (RyR) receptors. The RyR gating allows a rapid, massive, and highly regulated release of Ca2+ from the sarcoplasmic reticulum (SR). The release from triadic places generates a sarcomeric gradient of Ca2+ concentrations ([Ca2+]) depending on the distance of a subcellular region from the CRU. Upon release, the diffusing Ca2+ has multiple fates: binds to troponin C thus activating the contractile machinery, binds to classical sarcoplasmic Ca2+ buffers such as parvalbumin, adenosine triphosphate and, experimentally, fluorescent dyes, enters the mitochondria and the SR, or is recycled through the Na+/Ca2+ exchanger and store-operated Ca2+ entry (SOCE) mechanisms. To commemorate the 7th decade after being coined, we comprehensively and critically reviewed “old”, historical landmarks and well-established concepts, and blended them with recent advances to have a complete, quantitative-focused landscape of the ECC. We discuss the: 1) elucidation of the CRU structures at near-atomic resolution and its implications for functional coupling; 2) reliable quantification of peak sarcoplasmic [Ca2+] using fast, low affinity Ca2+ dyes and the relative contributions of the Ca2+-binding mechanisms to the whole concert of Ca2+ fluxes inside the fibre; 3) articulation of this novel quantitative information with the unveiled structural details of the molecular machinery involved in mitochondrial Ca2+ handing to understand how and how much Ca2+ enters the mitochondria; 4) presence of the SOCE machinery and its different modes of activation, which awaits understanding of its magnitude and relevance in situ; 5) pharmacology of the ECC, and 6) emerging topics such as the use and potential applications of super-resolution and induced pluripotent stem cells (iPSC) in ECC. Blending the old with the new works better!
Collapse
Affiliation(s)
- Pura Bolaños
- Laboratory of Cellular Physiology, Centre of Biophysics and Biochemistry, Venezuelan Institute for Scientific Research (IVIC), Caracas, Venezuela
| | - Juan C. Calderón
- Physiology and Biochemistry Research Group-PHYSIS, Faculty of Medicine, University of Antioquia, Medellín, Colombia
- *Correspondence: Juan C. Calderón,
| |
Collapse
|
2
|
Martelly I, Singabraya D, Vandebrouck A, Papy-Garcia D, Cognard C, Raymond G, Guillet-Deniau I, Courty J, Constantin B. Glycosaminoglycan mimetics trigger IP3-dependent intracellular calcium release in myoblasts. Matrix Biol 2010; 29:317-29. [PMID: 20193761 DOI: 10.1016/j.matbio.2010.02.002] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/23/2009] [Revised: 02/05/2010] [Accepted: 02/05/2010] [Indexed: 11/18/2022]
Abstract
Glycosaminoglycans (GAG) are sulfated polysaccharides that play an important role in regulating cell functions. GAG mimetics called RGTAs (for ReGeneraTing Agents) have been shown to stimulate tissue repair. In particular they accelerate myogenesis, in part via their heparin-mimetic property towards growth factors. RGTAs also increase activity of calcium-dependent intracellular protease suggesting an effect on calcium cellular homeostasis. This effect was presently investigated on myoblasts in vitro using one member of the RGTA family molecule named OTR4120. We have shown that OTR4120 or heparin induced transient increases of intracellular calcium concentration ([Ca(2+)]i) in pre-fusing myoblasts from both mouse SolD7 cell line and rat skeletal muscle satellite cells grown in primary culture by mobilising sarcoplasmic reticulum store. This [Ca(2+)]i was not mediated by ryanodine receptors but instead resulted from stimulation of the Inositol-3 phosphate-phospholipase C activation pathway. OTR4120-induced calcium transient was not mediated through an ATP, nor a tyrosine kinase, nor an acetylcholine receptor but principally through serotonin 5-HT2A receptor. This original finding shows that the GAG mimetic can induce calcium signal through serotonin receptors and the IP3 pathway may be relevant to its ability to favour myoblast differentiation. It supports a novel and unexpected function of GAGs in the regulation of calcium homeostasis.
Collapse
Affiliation(s)
- Isabelle Martelly
- Laboratoire de Recherche sur la Croissance Cellulaire, la Réparation et la Régénération Tissulaires (CRRET), UMR 7149-CNRS, Université Paris-Est Créteil, France.
| | | | | | | | | | | | | | | | | |
Collapse
|
3
|
Lofrano-Alves MS, Oliveira EL, Damiani CEN, Kassouf-Silva I, Fogaça RTH. Eugenol-induced contractions of saponin-skinned fibers are inhibited by heparin or by a ryanodine receptor blocker. Can J Physiol Pharmacol 2006; 83:1093-100. [PMID: 16462908 DOI: 10.1139/y05-104] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
The effects of eugenol on the sarcoplasmic reticulum (SR) and contractile apparatus of chemically skinned skeletal muscle fibers of the frog Rana catesbeiana were investigated. In saponin-skinned fibers, eugenol (5 mmol/L) induced muscle contractions, probably by releasing Ca(2+) from the SR. The Ca(2+)-induced Ca(2+) release blocker ruthenium red (10 micromol/L) inhibited both caffeine- and eugenol-induced muscle contractions. Ryanodine (200 micromol/L), a specific ryanodine receptor/Ca(2+) release channel blocker, promoted complete inhibition of the contractions induced by caffeine, but only partially blocked the contractions induced by eugenol. Heparin (2.5 mg/mL), an inositol 1,4,5-trisphosphate (InsP3) receptor blocker, strongly inhibited the contractions induced by eugenol but had only a small effect on the caffeine-induced contractions. Eugenol neither altered the Ca(2+) sensitivity nor the maximal force in Triton X-100 skinned muscle fibers. These data suggest that muscle contraction induced by eugenol involves at least 2 mechanisms of Ca(2+) release from the SR: one related to the activation of the ryanodine receptors and another through a heparin-sensitive pathway.
Collapse
Affiliation(s)
- Marco S Lofrano-Alves
- Departamento de Fisiologia, Setor de Ciências Biológicas, Centro Politécnico, Universidade Federal do Paraná, Curitiba, Paraná, Brazil
| | | | | | | | | |
Collapse
|
4
|
Jenniskens GJ, Veerkamp JH, van Kuppevelt TH. Heparan sulfates in skeletal muscle development and physiology. J Cell Physiol 2005; 206:283-94. [PMID: 15991249 DOI: 10.1002/jcp.20450] [Citation(s) in RCA: 29] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/12/2022]
Abstract
Recent years have seen an emerging interest in the composition of the skeletal muscle extracellular matrix (ECM) and in the developmental and physiological roles of its constituents. Many cell surface-associated and ECM-embedded molecules occur in highly organized spatiotemporal patterns, suggesting important roles in the development and functioning of skeletal muscle. Glycans are historically underrepresented in the study of skeletal muscle ECM, even though studies from up to 30 years ago have demonstrated specific carbohydrates and glycoproteins to be concentrated in neuromuscular junctions (NMJs). Changes in glycan profile and distribution during myogenesis and synaptogenesis hint at an active involvement of glycoconjugates in muscle development. A modest amount of literature involves glycoconjugates in muscle ion housekeeping, but a recent surge of evidence indicates that glycosylation defects are causal for many congenital (neuro)muscular disorders, rendering glycosylation essential for skeletal muscle integrity. In this review, we focus on a single class of ECM-resident glycans and their emerging roles in muscle development, physiology, and pathology: heparan sulfate proteoglycans (HSPGs), notably their heparan sulfate (HS) moiety.
Collapse
Affiliation(s)
- Guido J Jenniskens
- Department of Biochemistry 194, University Medical Center, NCMLS, Nijmegen, The Netherlands
| | | | | |
Collapse
|
5
|
Jenniskens GJ, Koopman WJH, Willems PHGM, Pecker I, Veerkamp JH, van Kuppevelt TH. Phenotypic knock out of heparan sulfates in myotubes impairs excitation-induced calcium spiking. FASEB J 2003; 17:878-80. [PMID: 12626439 DOI: 10.1096/fj.02-0572fje] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/19/2022]
Abstract
Little is known about the physiological functions of heparan sulfates (HSs), which are present in the basal lamina surrounding skeletal muscle fibers. Here, we present a new system in which HS is phenotypically knocked out by endogenous expression of epitope-specific anti-HS antibodies. Single-chain antibodies, containing an immunoglobulin leader peptide, were produced by using various expression systems. Antibodies were detected in the Golgi apparatus, the site of HS biosynthesis. Likewise, the HS-degrading enzyme heparanase was expressed. Endogenous expression of antibodies or heparanase in myoblasts resulted in HS-defective myotubes. Excitability and calcium kinetics of HS-defective myotubes were severely compromised, as determined by analysis of electrically induced calcium spikes via video-speed UV confocal laser scanning microscopy. Phenotypically knocking out of individual HS epitopes resulted in specific effects on excitability and calcium kinetics. These data indicate important roles for HSs in skeletal muscle calcium kinetics.
Collapse
Affiliation(s)
- Guido J Jenniskens
- Department of Biochemistry 194, University Medical Center, NCMLS, 6500 HB Nijmegen, The Netherlands
| | | | | | | | | | | |
Collapse
|
6
|
Launikonis BS, Barnes M, Stephenson DG. Identification of the coupling between skeletal muscle store-operated Ca2+ entry and the inositol trisphosphate receptor. Proc Natl Acad Sci U S A 2003; 100:2941-4. [PMID: 12601149 PMCID: PMC151445 DOI: 10.1073/pnas.0536227100] [Citation(s) in RCA: 83] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
Examination of store-operated Ca(2+) entry (SOC) in single, mechanically skinned skeletal muscle cells by confocal microscopy shows that the inositol 1,4,5-trisphosphate (IP(3)) receptor acts as a sarcoplasmic reticulum [Ca(2+)] sensor and mediates SOC by physical coupling without playing a key role in Ca(2+) release from internal stores, as is the case with various cell types in which SOC was investigated previously. The results have broad implications for understanding the mechanism of SOC that is essential for cell function in general and muscle function in particular. Moreover, the study ascribes an important role to the IP(3) receptors in skeletal muscle, the role of which with respect to Ca(2+) homeostasis was ill defined until now.
Collapse
|
7
|
Lamb GD, El-Hayek R, Ikemoto N, Stephenson DG. Effects of dihydropyridine receptor II-III loop peptides on Ca(2+) release in skinned skeletal muscle fibers. Am J Physiol Cell Physiol 2000; 279:C891-905. [PMID: 11003569 DOI: 10.1152/ajpcell.2000.279.4.c891] [Citation(s) in RCA: 21] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
In skeletal muscle fibers, the intracellular loop between domains II and III of the alpha(1)-subunit of the dihydropyridine receptor (DHPR) may directly activate the adjacent Ca(2+) release channel in the sarcoplasmic reticulum. We examined the effects of synthetic peptide segments of this loop on Ca(2+) release in mechanically skinned skeletal muscle fibers with functional excitation-contraction coupling. In rat fibers at physiological Mg(2+) concentration ([Mg(2+)]; 1 mM), a 20-residue skeletal muscle DHPR peptide [A(S(20)); Thr(671)-Leu(690); 30 microM], shown previously to induce Ca(2+) release in a triad preparation, caused only small spontaneous force responses in approximately 40% of fibers, although it potentiated responses to depolarization and caffeine in all fibers. The COOH-terminal half of A(S(20)) [A(S(10))] induced much larger spontaneous responses but also caused substantial inhibition of Ca(2+) release to both depolarization and caffeine. Both peptides induced or potentiated Ca(2+) release even when the voltage sensors were inactivated, indicating direct action on the Ca(2+) release channels. The corresponding 20-residue cardiac DHPR peptide [A(C(20)); Thr(793)-Ala(812)] was ineffective, but its COOH-terminal half [A(C(10))] had effects similar to A(S(20)). In the presence of lower [Mg(2+)] (0.2 mM), exposure to either A(S(20)) or A(C(10)) (30 microM) induced substantial Ca(2+) release. Peptide C(S) (100 microM), a loop segment reported to inhibit Ca(2+) release in triads, caused partial inhibition of depolarization-induced Ca(2+) release. In toad fibers, each of the A peptides had effects similar to or greater than those in rat fibers. These findings suggest that the A and C regions of the skeletal DHPR II-III loop may have important roles in vivo.
Collapse
Affiliation(s)
- G D Lamb
- School of Zoology, La Trobe University, Bundoora, Victoria 3083, Australia.
| | | | | | | |
Collapse
|
8
|
Ha TNV, Posterino GS, Fryer MW. Effects of terbutaline on force and intracellular calcium in slow-twitch skeletal muscle fibres of the rat. Br J Pharmacol 1999; 126:1717-24. [PMID: 10372813 PMCID: PMC1565959 DOI: 10.1038/sj.bjp.0702482] [Citation(s) in RCA: 35] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022] Open
Abstract
1. The effect of the alpha2-adrenoceptor agonist, terbutaline, was investigated on simultaneously measured force and intracellular free calcium ([Ca2+]i) in intact rat soleus muscle fibres, and on contractile protein function and Ca2+ content of the sarcoplasmic reticulum (SR) in skinned fibres. 2. Terbutaline (10 microM) had no significant effect on either resting force or [Ca2+]i. Exposure to terbutaline increased both the integral of the indo-1 ratio transient and peak twitch force by 37%. 3. At sub-maximal (10 Hz) stimulation frequencies, terbutaline accelerated force relaxation but had highly variable effects on tetanic force amplitude. The corresponding indo-1 ratio transients were significantly larger, and faster to decay than the controls. 4. Terbutaline increased tetanic force at near maximal stimulation frequencies (50 Hz) by increasing tetanic [Ca2+]i. Force relaxation was accelerated at this frequency with no significant change in the indo-1 ratio transient decay rate. 5. All of terbutaline's effects on force and indo-1 ratio transients in intact fibres were completely blocked and reversed by ICI 118551 (1 microM). 6. Mechanically skinned fibres isolated from intact muscles pre-treated with terbutaline showed no significant changes in SR Ca2+ content, myofilament [Ca2+]i-sensitivity or maximum force generating capacity. 7. The results suggest that terbutaline primarily modulates force by altering the amplitude and decay rate of the [Ca2+]i transient via phosphorylation of both the ryanodine receptor (RR) and the SR pump regulatory protein, phospholamban (PLB). The high variability of responses of slow-twitch muscles to beta2-agonists probably reflects individual differences in basal phosphorylation levels of PLB relative to that of RR.
Collapse
Affiliation(s)
- Tuyen N V Ha
- School of Physiology and Pharmacology, University of New South Wales, Sydney, New South Wales, 2052, Australia
| | - Giuseppe S Posterino
- School of Physiology and Pharmacology, University of New South Wales, Sydney, New South Wales, 2052, Australia
| | - Martin W Fryer
- School of Physiology and Pharmacology, University of New South Wales, Sydney, New South Wales, 2052, Australia
- Author for correspondence:
| |
Collapse
|
9
|
Uttenweiler D, Weber C, Fink RH. Mathematical modeling and fluorescence imaging to study the Ca2+ turnover in skinned muscle fibers. Biophys J 1998; 74:1640-53. [PMID: 9545029 PMCID: PMC1299511 DOI: 10.1016/s0006-3495(98)77877-4] [Citation(s) in RCA: 18] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/07/2023] Open
Abstract
A mathematical model was developed for the simulation of the spatial and temporal time course of Ca2+ ion movement in caffeine-induced calcium transients of chemically skinned muscle fiber preparations. Our model assumes cylindrical symmetry and quantifies the radial profile of Ca2+ ion concentration by solving the diffusion equations for Ca2+ ions and various mobile buffers, and the rate equations for Ca2+ buffering (mobile and immobile buffers) and for the release and reuptake of Ca2+ ions by the sarcoplasmic reticulum (SR), with a finite-difference algorithm. The results of the model are compared with caffeine-induced spatial Ca2+ transients obtained from saponin skinned murine fast-twitch fibers by fluorescence photometry and imaging measurements using the ratiometric dye Fura-2. The combination of mathematical modeling and digital image analysis provides a tool for the quantitative description of the total Ca2+ turnover and the different contributions of all interacting processes to the overall Ca2+ transient in skinned muscle fibers. It should thereby strongly improve the usage of skinned fibers as quantitative assay systems for many parameters of the SR and the contractile apparatus helping also to bridge the gap to the intact muscle fiber.
Collapse
Affiliation(s)
- D Uttenweiler
- Ruprecht-Karls-Universität Heidelberg, II Institute of Physiology, Germany
| | | | | |
Collapse
|
10
|
Posterino GS, Lamb GD. Investigation of the effect of inositol trisphosphate in skinned skeletal muscle fibres with functional excitation-contraction coupling. J Muscle Res Cell Motil 1998; 19:67-74. [PMID: 9477378 DOI: 10.1007/bf03257391] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/06/2023]
Abstract
The effect of inositol trisphosphate (IP3) was investigated in mechanically skinned fibres which had the endogenous level of sarcoplasmic reticulum (SR) Ca2+ and in which the normal excitation-contraction (E-C) coupling mechanism was still functional. Application of 50 or 100 microM IP3 failed to induce a detectable force response in any such skinned fibre from either the extensor digitorum longus muscle of the rat or iliofibularis muscle of the toad, irrespective of whether the fibre was: (a) in its normally polarized, resting state; (b) chronically depolarized to inactivate the voltage sensors; (c) paralysed with D600; or (d) depolarized to threshold for force activation. Furthermore, the size of the response to subsequent depolarization or exposure to caffeine (2mM) or reduced myoplasmic [Mg2+] indicated that little if any Ca2+ had been lost from the SR during the period of IP3 exposure (> or = 1 min). Also, IP3 did not induce a detectable force response when SR Ca2+ uptake was potently inhibited with 20 microM TBQ. Exposure to IP3 (50 microM) slightly potentiated the peak force response to depolarization in toad fibres, and this was probably because of an accompanying small increase in Ca2+ sensitivity of the contractile apparatus. These results appear inconsistent with the proposal that IP3 acts as the second messenger in E-C coupling in skeletal muscle.
Collapse
Affiliation(s)
- G S Posterino
- School of Zoology, La Trobe University, Bundoora, Victoria, Australia
| | | |
Collapse
|
11
|
Talon S, Huchet-Cadiou C, Léoty C. Negative inotropic effect of heparin on tension development in rat skinned skeletal muscle fibres. Eur J Pharmacol 1997; 327:33-40. [PMID: 9185833 DOI: 10.1016/s0014-2999(97)89675-6] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/04/2023]
Abstract
Heparin inhibits inositol trisphosphate receptors, particularly in smooth muscle, but its effect on skeletal muscle is controversial. Our study showed that heparin induced a decrease in the amplitude of 10 mM caffeine-induced contracture in slow and fast saponin-skinned fibres. Moreover, measurements on Triton X-100-skinned fibres in soleus muscle showed that heparin alone decreased maximal Ca2(+)-activated tension and Ca2+ sensitivity of contractile proteins, whereas no significant effect was observed in extensor digitorum longus muscle. However, in the presence of caffeine, heparin decreased maximal Ca2(+)-activated tension in both muscles. It would appear that the heparin-induced decrease in the amplitude of caffeine contracture in rat skeletal muscle was not related to a direct inhibition of Ca2+ release from sarcoplasmic reticulum but to a desensitising effect of heparin and caffeine on myofilaments.
Collapse
Affiliation(s)
- S Talon
- Laboratoire de Physiologie Générale, URA CNRS 1340, Faculté des Sciences et des Techniques, Nantes, France
| | | | | |
Collapse
|
12
|
Posterino GS, Lamb GD. Effects of reducing agents and oxidants on excitation-contraction coupling in skeletal muscle fibres of rat and toad. J Physiol 1996; 496 ( Pt 3):809-25. [PMID: 8930846 PMCID: PMC1160866 DOI: 10.1113/jphysiol.1996.sp021729] [Citation(s) in RCA: 44] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/03/2023] Open
Abstract
1. The mechanically skinned fibre technique was used to examine the role of oxidation-reduction in the control of Ca2+ release and contraction in rat and toad skeletal muscle fibres under physiological conditions of myoplasmic [Mg2+] and [ATP] and sarcoplasmic reticulum (SR) Ca2+ load. 2. None of the reducing agents, dithiothreitol (DTT, 10 mM), glutathione (GSH, 10 mM) or cysteine (1 and 5 mM), had any detectable effect on the peak force, duration or the total number of depolarization-induced responses that could be elicited in skinned fibres from either toad or rat muscle, except for a slight alteration in one case (GSH on the duration of the response in rat fibres) caused by an effect of the agent of the Ca2+ sensitivity of the contractile apparatus. 3. Application of the reactive disulphide, 2,2'-dithiodipyridine (DTDP, 100 microM), a potent oxidizing agent, never induced any measurable force response or noticeable depletion of SR Ca2+ in any fibre under the conditions used. When all Ca2+ uptake was prevented, DTDP treatment of rat fibres was found to cause a 2- to 3-fold increase in the low rate of Ca2+ "leak' from the SR. DTDP treatment also increased the responsiveness of toad muscle fibres to 1 or 2 mM caffeine. These effects could be largely reversed by treatment with DTT. These results indicate that oxidation of the Ca2+ release channel does not cause substantial channel opening under physiological conditions. 4. Depolarization-induced force responses in both rat and toad fibres were rapidly abolished in the presence of DTDP (10 or 100 microM), in a manner favoured by inactivation of the voltage sensors. The relatively impermeant oxidant, 5,5'-dithionitrobenzoic acid (DTNB, 100 microM), had an effect very similar to DTDP if applied intracellularly, but unlike DTDP, had little or no effect if applied extracellularly (at 5 mM) before skinning. Depolarization-induced responses could be restored by treatment with DTT (10 mM). Intracellular application of the sulfhydryl-alkylating agent, N-ethylmaleimide (NEM, 100 microM), had effects very similar to DTDP and DTNB. 5. These results are not consistent with the proposal that excitation-contraction coupling in skeletal muscle primarily involves the oxidative linkage of the voltage sensors to the Ca2+ release channels, but do show that oxidation of an intracellularly accessible site can interfere with the coupling, in a process made more sensitive by voltage sensor inactivation.
Collapse
Affiliation(s)
- G S Posterino
- School of Zoology, La Trobe University, Bundoora, Victoria, Australia
| | | |
Collapse
|
13
|
Martínez M, García MC, Farías JM, Cruzblanca H, Sánchez JA. Modulation of Ca2+ channels, charge movement and Ca2+ transients by heparin in frog skeletal muscle fibres. J Muscle Res Cell Motil 1996; 17:575-94. [PMID: 8906624 DOI: 10.1007/bf00124356] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/03/2023]
Abstract
This study is an investigation into the modulatory effects of heparin, a component of the extracellular matrix that binds to dihydropyridine receptors, on contraction and Ca2+ channels in frog skeletal muscle. Using tension and Ca2+ signal measurements in single intact skeletal muscle cells we have found that heparin (100-200 micrograms ml-1) substantially potentiates twitch and tetanic tension (55% and 28%, respectively). In contrast, heparin reduces the amplitude of K+ contractures. Heparin most likely potentiates twitch tension by prolonging action potentials. The ionic basis of this effect was investigated in voltage-clamp experiments. Membrane currents were monitored in voltage-clamped segments of single fibres using the triple Vaseline gap technique. We found that heparin partially blocks delayed rectifier potassium channels. The depressive effects of heparin on K+ contractures prompted us to investigate the effects of heparin on charge movement and Ca2+ currents (ICa) under voltage-clamp. Charge movement was measured using a subtraction procedure that employed a -20 mV control pulse from a holding potential of -100 mV. Heparin depresses the total charge by 25%. We propose that the reduction in the amplitude of potassium contractures is related to a partial blockade of charge movement. Extracellular heparin shifts the ICa-V relation toward more negative voltages and delays the deactivation of tail currents. Double pulse experiments revealed that conditioning depolarizations speed the activation of ICa during test depolarizations. Heparin does not affect this process. The primary action of heparin is to accelerate the activation of ICa during pulses not preceded by conditioning depolarizations. Overall, the kinetic effects of heparin on ICa would increase the Ca2+ influx associated with action potentials. However, mechanical and optical experiments performed in Ca(2+) -free solutions and in the presence of Ca2+ channel blockers revealed that twitch and tetanic potentiation occur even in the absence of Ca(2+) -influx.
Collapse
Affiliation(s)
- M Martínez
- Department of Pharmacology, Centro de Investigación y de Estudios Avanzados'del I.P.N., México, D.F., México
| | | | | | | | | |
Collapse
|
14
|
Gonzalez A, Caputo C. Ryanodine interferes with charge movement repriming in amphibian skeletal muscle fibers. Biophys J 1996; 70:376-82. [PMID: 8770214 PMCID: PMC1224936 DOI: 10.1016/s0006-3495(96)79581-4] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/02/2023] Open
Abstract
Cut twitch muscle fibers mounted in a triple Vaseline-gap chamber were used to study the effects of ryanodine on intramembranous charge movement, and in particular on the repriming of charge 1. Charge 1 repriming was measured either under steady-state conditions or by using a pulse protocol designed to study the time course of repriming. This protocol consisted of repolarizing the fibers to -100 mV from a holding potential of 0 mV, and then measuring the reprimed charge moving in the potential range between -40 and +20 mV. Ryanodine at a high concentration (100 microM) did not affect the maximum amount of movable charge 1 and charge 2, or their voltage dependence. This indicates that the alkaloid does not interact with the voltage sensor molecules. However, ryanodine did reduce the amount of reprimed charge 1 by approximately 60% suggesting the possibility of a retrograde interaction between ryanodine receptors and voltage sensors.
Collapse
Affiliation(s)
- A Gonzalez
- Laboratorio de Biofisica del Musculo, Instituto Venezolano de Investigaciones Cientificas, Caracas, Venezuela
| | | |
Collapse
|
15
|
Stephenson DG, Lamb GD, Stephenson GM, Fryer MW. Mechanisms of excitation-contraction coupling relevant to skeletal muscle fatigue. ADVANCES IN EXPERIMENTAL MEDICINE AND BIOLOGY 1995; 384:45-56. [PMID: 8585471 DOI: 10.1007/978-1-4899-1016-5_4] [Citation(s) in RCA: 13] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/31/2023]
Affiliation(s)
- D G Stephenson
- School of Zoology, La Trobe University, Bundoora, Victoria, Australia
| | | | | | | |
Collapse
|