Kawata H
Jpn J Physiol. 1985;35(6):953-72. doi: 10.2170/jjphysiol.35.953.
Some features of the electrically induced contracture were investigated by means of the partition polarization method in the toe muscles of a bullfrog. Under the current clamp condition and in the presence of tetrodotoxin, a biphasic contracture was induced by strong depolarizing pulses, 1 sec, in duration. The contracture was depressed either by lengthening the pulse interval or by reducing the external calcium concentration. Furthermore, the contracture was augmented by applying conditioning depolarization and inhibited by conditioning hyperpolarization without accompanying any noticeable changes in the test depolarization. Caffeine at a concentration of 1 mM depressed the inhibitory effect of pre-hyperpolarization. Strong hyperpolarizing pulses had no effect on the caffeine contracture, whereas a similar pre-hyperpolarization markedly suppressed the phenomenon on the post-contracture potentiation of twitch, induced by a powerful sustained depolarization. From these results it was suggested that calcium ions in the vicinity of the myoplasmic site of the transverse tubular membrane may play some role in generating and regulating the contracture. The possibility of direct contribution of calcium entering from the cell exterior in contracture generation, especially for the slow component, and its regulation was also discussed.
采用分区极化法对牛蛙趾肌电诱导挛缩的一些特征进行了研究。在电流钳制条件下且存在河豚毒素时，持续1秒的强去极化脉冲可诱发双相挛缩。通过延长脉冲间隔或降低细胞外钙浓度，挛缩会受到抑制。此外，施加条件性去极化可增强挛缩，而条件性超极化则会抑制挛缩，同时测试去极化没有伴随任何明显变化。浓度为1 mM的咖啡因可抑制预超极化的抑制作用。强超极化脉冲对咖啡因挛缩没有影响，而类似的预超极化则明显抑制了由强力持续去极化诱导的挛缩后收缩增强现象。从这些结果推测，横管膜肌浆部位附近的钙离子可能在挛缩的产生和调节中发挥一定作用。还讨论了细胞外进入的钙直接参与挛缩产生特别是慢成分产生及其调节的可能性。
