Caffeine-induced Ca2+ sparks in mouse ventricular myocytes

2000 ◽  
Vol 278 (2) ◽  
pp. H666-H669 ◽  
Author(s):  
Michael Ritter ◽  
Zhi Su ◽  
Kenneth W. Spitzer ◽  
Hideyuki Ishida ◽  
William H. Barry
Keyword(s):  
Sarcoplasmic Reticulum ◽  
Cell Surface ◽  
Ryanodine Receptor ◽  
Ventricular Myocytes ◽  
Surface Membrane ◽  
Release Channel ◽  
Whole Cell ◽  
Cell Surface Membrane ◽  
Naturally Occurring ◽  
Intracellular Ca

Ca2+ sparks are spatially localized intracellular Ca2+ release events that were first described in 1993. Sparks have been ascribed to sarcoplasmic reticulum Ca2+ release channel (ryanodine receptor, RyR) opening induced by Ca2+ influx via L-type Ca2+ channels or by spontaneous RyR openings and have been thought to reflect Ca2+ release from a cluster of RyR. Here we describe a pharmacological approach to study sparks by exposing ventricular myocytes to caffeine with a rapid solution-switcher device. Sparks under these conditions have properties similar to naturally occurring sparks in terms of size and intracellular Ca2+ concentration ([Ca2+]i) amplitude. However, after the diffusion of caffeine, sparks first appear close to the cell surface membrane before coalescing to produce a whole cell transient. Our results support the idea that a whole cell [Ca2+]i transient consists of the summation of sparks and that Ca2+ sparks consist of the opening of a cluster of RyR and confirm that characteristics of the cluster rather than the L-type Ca2+ channel-RyR relation determine spark properties.

scholarly journals cADP ribose and [Ca2+]iregulation in rat cardiac myocytes

2000 ◽  
Vol 279 (4) ◽  
pp. H1482-H1489 ◽  
Author(s):  
Y. S. Prakash ◽  
Mathur S. Kannan ◽  
Timothy F. Walseth ◽  
Gary C. Sieck
Keyword(s):  
Electrical Stimulation ◽  
Sarcoplasmic Reticulum ◽  
Confocal Microscopy ◽  
Real Time ◽  
Cardiac Myocytes ◽  
Ryanodine Receptor ◽  
Ventricular Myocytes ◽  
Adult Rat ◽  
Intracellular Ca ◽  
Rat Cardiac Myocytes

cADP ribose (cADPR)-induced intracellular Ca2+ concentration ([Ca2+]i) responses were assessed in acutely dissociated adult rat ventricular myocytes using real-time confocal microscopy. In quiescent single myocytes, injection of cADPR (0.1–10 μM) induced sustained, concentration-dependent [Ca2+]i responses ranging from 50 to 500 nM, which were completely inhibited by 20 μM 8-amino-cADPR, a specific blocker of the cADPR receptor. In myocytes displaying spontaneous [Ca2+]i waves, increasing concentrations of cADPR increased wave frequency up to ∼250% of control. In electrically paced myocytes (0.5 Hz, 5-ms duration), cADPR increased the amplitude of [Ca2+]i transients in a concentration-dependent fashion, up to 150% of control. Administration of 8-amino-cADPR inhibited both spontaneous waves as well as [Ca2+]i responses to electrical stimulation, even in the absence of exogenous cADPR. However, subsequent [Ca2+]i responses to 5 mM caffeine were only partially inhibited by 8-amino-cADPR. In contrast, even under conditions where ryanodine receptor (RyR) channels were blocked with ryanodine, high cADPR concentrations still induced an [Ca2+]i response. These results indicate that in cardiac myocytes, cADPR induces Ca2+ release from the sarcoplasmic reticulum through both RyR channels and via mechanisms independent of RyR channels.

Interaction of Bupivacaine and Tetracaine with the Sarcoplasmic Reticulum Ca2+Release Channel of Skeletal and Cardiac Muscles 

1999 ◽  
Vol 90 (3) ◽  
pp. 835-843 ◽  
Author(s):  
Hirochika Komai ◽  
Andrew J. Lokuta
Keyword(s):  
Skeletal Muscle ◽  
Sarcoplasmic Reticulum ◽  
Cardiac Muscle ◽  
Ryanodine Receptor ◽  
Local Anesthetic ◽  
Local Anesthetics ◽  
Specific Effect ◽  
Receptor Activity ◽  
Maximal Inhibition ◽  
Release Channel

Background Although various local anesthetics can cause histologic damage to skeletal muscle when injected intramuscularly, bupivacaine appears to have an exceptionally high rate of myotoxicity. Research has suggested that an effect of bupivacaine on sarcoplasmic reticulum Ca2+ release is involved in its myotoxicity, but direct evidence is lacking. Furthermore, it is not known whether the toxicity depends on the unique chemical characteristics of bupivacaine and whether the toxicity is found only in skeletal muscle. Methods The authors studied the effects of bupivacaine and the similarly lipid-soluble local anesthetic, tetracaine, on the Ca2+ release channel-ryanodine receptor of sarcoplasmic reticulum in swine skeletal and cardiac muscle. [3H]Ryanodine binding was used to measure the activity of the Ca2+ release channel-ryanodine receptors in microsomes of both muscles. Results Bupivacaine enhanced (by two times at 5 mM) and inhibited (66% inhibition at 10 mM) [3H]ryanodine binding to skeletal muscle microsomes. In contrast, only inhibitory effects were observed with cardiac microsomes (about 3 mM for half-maximal inhibition). Tetracaine, which inhibits [3H]ryanodine binding to skeletal muscle microsomes, also inhibited [3H]ryanodine binding to cardiac muscle microsomes (half-maximal inhibition at 99 microM). Conclusions Bupivacaine's ability to enhance Ca2+ release channel-ryanodine receptor activity of skeletal muscle sarcoplasmic reticulum most likely contributes to the myotoxicity of this local anesthetic. Thus, the pronounced myotoxicity of bupivacaine may be the result of this specific effect on Ca2+ release channel-ryanodine receptor superimposed on a nonspecific action on lipid bilayers to increase the Ca2+ permeability of sarcoplasmic reticulum membranes, an effect shared by all local anesthetics. The specific action of tetracaine to inhibit Ca2+ release channel-ryanodine receptor activity may in part counterbalance the nonspecific action, resulting in moderate myotoxicity.

Steady-state twitch Ca2+ fluxes and cytosolic Ca2+ buffering in rabbit ventricular myocytes

1996 ◽  
Vol 270 (1) ◽  
pp. C192-C199 ◽  
Author(s):  
L. M. Delbridge ◽  
J. W. Bassani ◽  
D. M. Bers
Keyword(s):  
Steady State ◽  
Sarcoplasmic Reticulum ◽  
Voltage Clamp ◽  
Ventricular Myocytes ◽  
Cell Voltage ◽  
Whole Cell ◽  
Rabbit Ventricular Myocytes ◽  
The Mean ◽  
State Contraction ◽  
Caffeine Contractures

Intracellular Ca2+ ([Ca2+]i) transients and transsarcolemmal Ca2+ currents were measured in indo 1-loaded isolated rabbit ventricular myocytes during whole cell voltage clamp to quantitate the components of cytosolic Ca2+ influx and to describe the dynamic aspects of cytosolic Ca2+ buffering during steady-state contraction (0.5 Hz, 22 degrees C). Sarcolemmal Ca2+ influx was directly measured from the integrated Ca2+ current (Ica) recorded during the clamp (158 +/- 10 attomoles; amol). Sarcoplasmic reticulum (SR) Ca2+ content was determined from the integrated electrogenic Na+/Ca2+ exchange current (Ix) induced during rapid application and sustained exposure of cells to caffeine to elicit the release of the SR Ca2+ load (1,208 +/- 170 amol). The mean steady-state SR Ca2+ load was calculated to be 87 +/- 13 microM (mumol/l nonmitochondrial cytosolic volume). Ca2+ influx via Ica represented approximately 14% of the stored SR Ca2+ and 23% of the total cytosolic Ca2+ flux during a twitch (47 +/- 6 microM). Comparison of electrophysiologically measured Ca2+ fluxes with Ca2+ transients yields apparent buffering values of 60 for caffeine contractures and 110 for twitches (delta Ca2+ total/delta Ca2+ free). This is consistent with the occurrence of "active" buffering of cytosolic Ca2+ by SR Ca2+ uptake during the twitch.

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