Depressed ryanodine receptor activity increases variability and duration of the systolic Ca2+ transient in rat ventricular myocytes.
Sarcoplasmic reticulum (SR) Ca2+ release, through the ryanodine receptor (RyR), is essential for the systolic Ca2+ transient and thus the cardiac contractile function. The aim of this study was to examine the effects on the spatial organization of the systolic Ca2+ transient of depressing RyR open probability (P(o)) with tetracaine or intracellular acidification. Voltage-clamped, fluo-3-loaded myocytes were studied using confocal microscopy. Depressing RyR P(o) increased the variability of the Ca2+ transient amplitude between different regions of the cell. This variability often produced alternans with a region producing large and small transients alternately. In addition, the raising phase of the Ca2+ transient became biphasic. The initial phase was constant but the second was variable and propagated as a wave through part of the cell. That both phases involved SR Ca2+ release was shown by their reduction by caffeine. Regional [Ca2+]i alternans was accompanied by a much smaller degree of alternans at the whole cell level. We suggest that, in tetracaine or acidosis, the initial phase of the Ca2+ transient results from Ca2+ release via RyRs directly activated by adjacent L-type Ca2+ channels. At some sites, this will activate neighboring RyRs and a Ca2+ wave will propagate via activation of other RyRs. This work is the first demonstration that decreased RyR P(o) alone can produce disarray of the Ca2+ release process and initiate alternans.
D000818:Animals; D020013:Calcium Signaling / Q000187:drug effects; D002478:Cells, Cultured; D006352:Heart Ventricles / Q000166:cytology / Q000378:metabolism*; D006863:Hydrogen-Ion Concentration; D007700:Kinetics; D018613:Microscopy, Confocal; D009200:Myocardial Contraction; D018408:Patch-Clamp Techniques; D051381:Rats; D017208:Rats, Wistar; D019837:Ryanodine Receptor Calcium Release Channel / Q000378:metabolism*; D012519:Sarcoplasmic Reticulum / Q000378:metabolism; D013599:Systole; D013748:Tetracaine / Q000494:pharmacology; D016276:Ventricular Function
D019837:Ryanodine Receptor Calcium Release Channel; D013748:Tetracaine