Takauji M, Tsutsu M, Kanaya H, Nagai T
Jpn J Physiol. 1985;35(4):613-27. doi: 10.2170/jjphysiol.35.613.
The inactivation of potassium (K) contractures induced by prolonged conditioning depolarization and repriming after 190 mM K+ contractures were studied at both room and low temperatures using frog single twitch muscle fibers. Effects of conditioning K+ depolarization and external Ca2+ reduction on the biphasic K contractures were also studied. When the conditioning depolarization with 15-30 mM K+ was prolonged, the peak tension of test 190 mM K+ contractures was inhibited in parallel with the shortening of plateau duration at both room and low temperatures. Such parallel changes were also observed during the early stage of repriming after 190 mM K+ contracture at both temperatures. On the other hand, the peak tension of the secondary component of the test 80 mM K+ contractures was rather potentiated by the conditioning depolarization, even though the time course of the component was markedly shortened. The foregoing changes were also illustrated in a diagramatic way. These results suggested that the peak tension and the time course of the test K contractures after conditioning depolarization and during repriming may be determined by a balance between the activation and the inactivation processes of the contractures. This view is supported by the results obtained under conditions in which the concentration of external Ca2+ was reduced. Furthermore, based on additional experimental results, it was suggested that the initial component is not accompanied by an inactivation process and that Ca uptake by sarcoplasmic reticulum may partially contribute to determining the spontaneous relaxation phase of the secondary component, at least at room temperature.
在室温和低温条件下，使用青蛙单收缩肌纤维研究了长时间条件性去极化诱导的钾（K）挛缩的失活以及190 mM K⁺挛缩后的再激发情况。还研究了条件性K⁺去极化和细胞外Ca²⁺减少对双相K挛缩的影响。当用15 - 30 mM K⁺进行的条件性去极化时间延长时，在室温和低温下，测试的190 mM K⁺挛缩的峰值张力均与平台期持续时间的缩短平行受到抑制。在两个温度下，190 mM K⁺挛缩后的再激发早期也观察到了这种平行变化。另一方面，尽管80 mM K⁺挛缩测试的第二成分的时间进程明显缩短，但其峰值张力却因条件性去极化而增强。上述变化也以图表形式进行了说明。这些结果表明，条件性去极化后和再激发期间测试K挛缩的峰值张力和时间进程可能由挛缩的激活和失活过程之间的平衡决定。细胞外Ca²⁺浓度降低条件下获得的结果支持了这一观点。此外，基于额外的实验结果表明，初始成分不伴随失活过程，并且肌浆网对Ca的摄取可能至少在室温下部分有助于确定第二成分的自发松弛阶段。
