Altered cardiac sarcoplasmic reticulum function of intact myocytes of rat ventricle during metabolic inhibition

Abstract

Changes in the behavior of the sarcoplasmic reticulum (SR) in rat ventricular myocytes were investigated under conditions of metabolic inhibition using laser-scanning confocal microscopy to measure intracellular Ca2+ and the perforated patch-clamp technique to measure SR Ca2+ content. Metabolic inhibition had several effects on SR function, including reduced frequency of spontaneous releases of Ca2+ (sparks and waves of Ca2+-induced Ca2+ release), increased SR Ca2+ content (79.4±5.7 to 115.2±6.6 μmol/L cell volume [mean±SEM; P<0.001]), and, after a wave of Ca2+ release, slower reuptake of Ca2+ into the SR (rate constant of fall of Ca2+ reduced from 8.5±1.1 s-1 in control to 5.2±0.4 s-1 in metabolic inhibition [P<0.01]). Inhibition of L-type Ca2+ channels with Cd2+ (100 μmol/L) did not reproduce the effects of metabolic inhibition on spontaneous Ca2+ sparks. These results are evidence of inhibition of both Ca2+ release and reuptake mechanisms. Reduced frequency of release could be attributable to either of these effects, but the increased SR Ca2+ content at the time of reduced frequency of spontaneous release of Ca2+ shows that the dominant effect of metabolic inhibition is to inhibit release of Ca2+ from the SR, allowing the accumulation of greater than normal amounts of Ca2+. In the context of ischemia, this extra accumulation of Ca2+ would present a risk of potentially arrhythmogenic, spontaneous release of Ca2+ on reperfusion of the tissue.