Valdeolmillos M, Eisner D A
Circ Res. 1985 Mar;56(3):452-6. doi: 10.1161/01.res.56.3.452.
Prolonged exposure to high concentrations of strophanthidin produces an initial increase followed by a subsequent decrease of twitch tension. The slow decrease is termed calcium overload. The aim of the present work was to investigate the effects of ryanodine (an inhibitor of calcium release from the sarcoplasmic reticulum) on calcium-overloaded sheep cardiac Purkinje fibers. The fibers were voltage-clamped, and tension was measured while monitoring the intracellular calcium concentration with the photoprotein aequorin. When strophanthidin (10 microM) was applied to produce calcium overload, a depolarizing pulse produced twitch, and tonic components of tension and repolarization produced an aftercontraction. These components of tension were accompanied by corresponding increases of aequorin light. Ryanodine (1 microM) gave a transient increase of twitch tension. The twitch then decreased to very low levels. The aftercontraction and its corresponding aequorin light signal decreased monotonically on application of ryanodine. It has been suggested that the fall of force in calcium overload may be due to random diastolic release of calcium from the sarcoplasmic reticulum interfering with subsequent systolic calcium release. We suggest that the positive inotropic effect of ryanodine can be explained if ryanodine decreases the diastolic release of calcium. The transient positive inotropic effect of ryanodine reported here is therefore consistent with the hypothesis that the fall of force in calcium overload is due to diastolic calcium oscillations.
长时间暴露于高浓度毒毛花苷会使抽搐张力先升高，随后降低。这种缓慢降低被称为钙超载。本研究的目的是研究ryanodine（一种肌浆网钙释放抑制剂）对钙超载绵羊心脏浦肯野纤维的影响。对纤维进行电压钳制，在用电发光蛋白水母发光蛋白监测细胞内钙浓度的同时测量张力。当应用毒毛花苷（10微摩尔）产生钙超载时，一个去极化脉冲会产生抽搐，张力的强直成分和复极化会产生后收缩。这些张力成分伴随着水母发光蛋白光的相应增加。Ryanodine（1微摩尔）使抽搐张力短暂增加。然后抽搐张力降至非常低的水平。应用ryanodine后，后收缩及其相应的水母发光蛋白光信号单调下降。有人提出，钙超载时力的下降可能是由于肌浆网中钙的随机舒张期释放干扰了随后的收缩期钙释放。我们认为，如果ryanodine减少钙的舒张期释放，就可以解释ryanodine的正性肌力作用。因此，这里报道的ryanodine的短暂正性肌力作用与钙超载时力的下降是由于舒张期钙振荡这一假设是一致的。
