The mechanism of Ca release from sarcoplasmic reticulum induced by rapid cooling and its physiological meaning.

钙离子从SR释放是由钙离子内流作为钙电流触发的，这被称为钙诱导的钙释放（CICR）。另一方面，快速降温使SR中的钙释放，称为快速冷却钙释放（RCCR）。我们用水母发光蛋白研究了雪貂心室肌RCCR的机制。从30^0 ℃快速冷却至4^0 ℃以下，细胞内Ca浓度瞬时增加，但不伴随动作电位。钾浓度的变化对RCCR没有影响。在ryanodine处理的制剂中未观察到RCCR。因此，在快速冷却的Ca源是SR和RCCR不是由于膜去极化。快速冷却释放的Ca量不受快速冷却前的Ca浓度的影响。在无钠溶液中（Li和TMA替代），RCCR被抑制，但在无钠溶液中RCCR后立即施用咖啡因，释放的Ca比RCCR时多，表明RCCR的机制与咖啡因诱导的Ca释放机制不同。钠钙交换抑制剂和钙泵抑制剂对钙信号的衰减有轻微的抑制作用，而钌红则明显抑制钙信号的衰减。因此，在4^0 C时线粒体可能有足够的Ca被转运。这些结果表明，快速冷却可使SR释放Ca，而不引起膜电位的显著变化，是一种评价SR中Ca积累的有效方法。

The release of Ca from the SR is triggered by an influx of Ca as Ca current, which is called Ca-induced Ca release (CICR). On the other hand, rapid lowering the temperatrure of the bathing solution releases Ca from the SR, which is called rapid cooling Ca release (RCCR). We investigated the mechanism of RCCR in ferret ventricular muscles using aequorin. Rapid cooling from 30^0 to below 4^0 transiently increased intracellular Ca concentration without accompanying action potential. RCCR was not influenced by changing K concentration in the solution. RCCR was not observed in the ryanodine-treated preparations. Therefore, the source of Ca in rapid cooling is the SR and RCCR is not due to a membrane depolarization. The amount of Ca released by rapid cooling was not influenced by the Ca concentration just before the rapid cooling. RCCR was inhibited in Na-free solutions (Li and TMA replacement) but the application of caffeine just after the RCCR in Na-free solutions released more Ca than that in the RCCR.The result suggests that the mechanism of RCCR is different from that of caffeine-induced Ca release. The decay of Ca singal at 4^0C was slightly inhibited by the inhibitors of Na-Ca exchanger and the Ca pump of the SR.However, ruthenium red markedly inhibited the decay of Ca signal. Therefore, sufficient Ca might be transported by mitochondria at 4^0C.These results suggest that rapid cooling releases Ca from SR without a significant membrane potential change and is an useful method to assess the accumulated Ca in SR.