Role of local Ca2+ domains in activation of Ca(2+)-induced Ca2+ release in crayfish muscle fibers

1993 ◽  
Vol 264 (6) ◽  
pp. C1505-C1512 ◽  
Author(s):  
S. Gyorke ◽  
P. Palade
Keyword(s):  
Sarcoplasmic Reticulum ◽  
Cardiac Muscle ◽  
Binding Site ◽  
Equal Access ◽  
Crayfish Muscle ◽  
Simultaneous Measurements ◽  
Indicator Analysis ◽  
Dependent Processes ◽  
Ca2 Channels

Simultaneous measurements were made of crayfish muscle Ca2+ currents (ICa) and the intracellular Ca2+ transients they elicit due to Ca(2+)-induced Ca2+ release (CICR) from the sarcoplasmic reticulum (SR). Ca2+ concentration ([Ca2+]) elevations produced by Ca2+ entry via ICa were much more effective in triggering CICR than were ongoing release or homogeneous elevations of Ca2+ produced by photolysis of caged Ca2+. This suggests that [Ca2+] gradients exist when Ca2+ is elevated by ICa and that, during Ca2+ entry, [Ca2+] at the activation site of the release channels must be much greater than spatially averaged [Ca2+] reported by the indicator. Analysis of voltage dependencies of ICa inactivation and SR Ca2+ release suggest that both Ca(2+)-dependent processes are controlled by ICa via the nearest T tubule Ca2+ channel rather than by total ICa entry. The contribution of SR Ca2+ release to ICa inactivation studied with a two-pulse protocol was less than predicted if Ca2+ derived from SR Ca2+ release and from T tubule Ca2+ channels have equal access to the Ca2+ binding site controlling ICa inactivation. These results can be explained in terms of a scheme where sites for release activation and ICa inactivation are located in the same junctional gap subdomain, closer to the cytoplasmic mouth of the T tubule Ca2+ channel than to the cytoplasmic mouth of the SR Ca2+ release channels. Such a scheme could provide an explanation for the graded nature and selective control of CICR in this preparation as well as in vertebrate cardiac muscle.

Differential Ca2+ sensitivity of skeletal and cardiac muscle ryanodine receptors in the presence of calmodulin

2000 ◽  
Vol 279 (3) ◽  
pp. C724-C733 ◽  
Author(s):  
Bradley R. Fruen ◽  
Jennifer M. Bardy ◽  
Todd M. Byrem ◽  
Gale M. Strasburg ◽  
Charles F. Louis
Keyword(s):  
Skeletal Muscle ◽  
Sarcoplasmic Reticulum ◽  
Cardiac Muscle ◽  
Ryanodine Receptors ◽  
Cross Linking ◽  
Release Channel ◽  
Channel Activation ◽  
Functional Interactions ◽  
Ryr2 Channel

Calmodulin (CaM) activates the skeletal muscle ryanodine receptor Ca2+ release channel (RyR1) in the presence of nanomolar Ca2+ concentrations. However, the role of CaM activation in the mechanisms that control Ca2+ release from the sarcoplasmic reticulum (SR) in skeletal muscle and in the heart remains unclear. In media that contained 100 nM Ca2+, the rate of45Ca2+ release from porcine skeletal muscle SR vesicles was increased approximately threefold in the presence of CaM (1 μM). In contrast, cardiac SR vesicle45Ca2+ release was unaffected by CaM, suggesting that CaM activated the skeletal RyR1 but not the cardiac RyR2 channel isoform. The activation of RyR1 by CaM was associated with an approximately sixfold increase in the Ca2+ sensitivity of [3H]ryanodine binding to skeletal muscle SR, whereas the Ca2+ sensitivity of cardiac SR [3H]ryanodine binding was similar in the absence and presence of CaM. Cross-linking experiments identified both RyR1 and RyR2 as predominant CaM binding proteins in skeletal and cardiac SR, respectively, and [35S]CaM binding determinations further indicated comparable CaM binding to the two isoforms in the presence of micromolar Ca2+. In nanomolar Ca2+, however, the affinity and stoichiometry of RyR2 [35S]CaM binding was reduced compared with that of RyR1. Together, our results indicate that CaM activates RyR1 by increasing the Ca2+ sensitivity of the channel, and further suggest differences in CaM's functional interactions with the RyR1 and RyR2 isoforms that may potentially contribute to differences in the Ca2+ dependence of channel activation in skeletal and cardiac muscle.

Role of calmodulin methionine residues in mediating productive association with cardiac ryanodine receptors

2006 ◽  
Vol 290 (2) ◽  
pp. H794-H799 ◽  
Author(s):  
Edward M. Balog ◽  
Laura E. Norton ◽  
David D. Thomas ◽  
Bradley R. Fruen
Keyword(s):  
Sarcoplasmic Reticulum ◽  
Cardiac Muscle ◽  
Ryanodine Receptor ◽  
Ryanodine Receptors ◽  
Release Channel ◽  
Site Specific ◽  
High Affinity ◽  
Methionine Residues ◽  
Cardiac Ryanodine Receptor

Calmodulin (CaM) binds to the cardiac ryanodine receptor Ca2+ release channel (RyR2) with high affinity and may act as a regulatory channel subunit. Here we determine the role of CaM Met residues in the productive association of CaM with RyR2, as assessed via determinations of [3H]ryanodine and [35S]CaM binding to cardiac muscle sarcoplasmic reticulum (SR) vesicles. Oxidation of all nine CaM Met residues abolished the productive association of CaM with RyR2. Substitution of the COOH-terminal Mets of CaM with Leu decreased the extent of CaM inhibition of cardiac SR (CSR) vesicle [3H]ryanodine binding. In contrast, replacing the NH2-terminal Met of CaM with Leu increased the concentration of CaM required to inhibit CSR [3H]ryanodine binding but did not alter the extent of inhibition. Site-specific substitution of individual CaM Met residues with Gln demonstrated that Met124 was required for both high-affinity CaM binding to RyR2 and for maximal CaM inhibition. These results thus identify a Met residue critical for the productive association of CaM with RyR2 channels.

Role of L-type Ca2+ channels, sarcoplasmic reticulum and Rho kinase in rat basilar artery contractile properties in a new model of subarachnoid hemorrhage

2015 ◽  
Vol 72 ◽  
pp. 64-72 ◽  
Author(s):  
Juan José Egea-Guerrero ◽  
Francisco Murillo-Cabezas ◽  
María Ángeles Muñoz-Sánchez ◽  
Angel Vilches-Arenas ◽  
Cristina Porras-González ◽  
...  
Keyword(s):  
Subarachnoid Hemorrhage ◽  
Sarcoplasmic Reticulum ◽  
Basilar Artery ◽  
Rho Kinase ◽  
Contractile Properties ◽  
New Model ◽  
Ca2 Channels

Na+-Ca2+ exchange contributes to increase of cytosolic Ca2+ concentration during depolarization in heart muscle

1986 ◽  
Vol 250 (4) ◽  
pp. C651-C656 ◽  
Author(s):  
S. S. Sheu ◽  
V. K. Sharma ◽  
A. Uglesity
Keyword(s):  
Sarcoplasmic Reticulum ◽  
Channel Blocker ◽  
Ventricular Myocytes ◽  
Transport Systems ◽  
High K ◽  
K Concentration ◽  
Cardiac Excitation ◽  
Ca2 Channels ◽  
Isolated Rat

The possible role of Na+-Ca2+ exchange in contributing to depolarization-induced increase in cytosolic Ca2+ concentration ([Ca2+]i) of isolated rat ventricular myocytes was investigated. Measured with the Ca2+-sensitive indicator quin 2, [Ca2+]i increased from 177 +/- 12 (mean +/- SE, n = 11) to 468 +/- 41 nM when cells were depolarized with solutions containing 50 mM KCl [high extracellular K+ concentration ([K+]o)]. Approximately 73% of this high-[K+]o-induced increase in [Ca2+]i was abolished by the Ca2+ channel blocker verapamil (5 microM). For cells pretreated with 10 mM caffeine to deplete the Ca2+ stored in sarcoplasmic reticulum, 50 mM KCl still produced an increase in [Ca2+]i, even in the presence of 5 microM verapamil. However, if extracellular Na+ was replaced by Li+ or tris(hydroxymethyl)aminomethane, this increase was completely abolished. The results suggest that, in addition to voltage-sensitive Ca2+ channels, voltage-sensitive Na+-Ca2+ exchange can also contribute to the increase in [Ca2+]i on depolarization. Therefore both Ca2+ transport systems may play important roles in regulating cardiac excitation and contraction.

Anchorfibers and the Topography of Junctional SR

1977 ◽  
Vol 35 ◽  
pp. 582-583
Author(s):  
James Junker ◽  
Joachim R. Sommer
Keyword(s):  
Sarcoplasmic Reticulum ◽  
Cardiac Muscle ◽  
Single Filament ◽  
Relaxation Cycle ◽  
10 Nm Filaments ◽  
Junctional Sarcoplasmic Reticulum

Junctional sarcoplasmic reticulum (JSR) in all its forms (extended JSR, JSR of couplings, corbular SR) in both skeletal and cardiac muscle is always located at the Z - I regions of the sarcomeres. The Z tubule is a tubule of the free SR (non-specialized SR) which is consistently located at the Z lines in cardiac muscle (1). Short connections between JSR and Z lines have been described (2), and bundles of filaments at Z lines have been seen in skeletal (3) and cardiac (4) muscle. In opossum cardiac muscle, we have seen bundles of 10 nm filaments stretching across interfibrillary spaces and adjacent myofibrils with extensions to the plasma- lemma in longitudinal (Fig. 1) and transverse (Fig. 2) sections. Only an occasional single filament is seen elsewhere along a sarcomere. We propose that these filaments represent anchor fibers that maintain the observed invariant topography of the free SR and JSR throughout the contraction-relaxation cycle.

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