Calcium action potentials in rat fast-twitch and slow-twitch muscle fibres.
Calcium action potentials in rat fast-twitch and slow-twitch muscle fibres.
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大鼠快肌纤维和慢肌纤维的钙动作电位。
DOI：
10.1113/jphysiol.1983.sp014516
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发表时间：
1983
期刊：
影响因子：
--
通讯作者：
Stefani,E
中科院分区：
文献类型：
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作者：
Chiarandini,DJ;Stefani,E
在大鼠趾长伸肌(E.D.L.)的抽动纤维上诱发慢动作电位。和比目鱼肌，在显著降低肌肉纤维的氯和钾电导之后。将肌肉暴露在不含氯的生理盐水中，其中甲烷磺酸盐取代氯，从而消除氯的电导。在无氯生理盐水中加入四乙基铵(TEA)和3，4-二氨基吡啶(3，4-DAP)或在含Cs和TEA的生理盐水中孵育过夜，可降低钾电导。TEA和3，4-DAP可明显阻断延迟整流。相比之下，内向整流只有茶才能阻断。脉冲幅度增大引起慢反应，阈值为-30~-10 mV，峰值为50~60 mV。在E.D.L。肌肉反应的时间过程在脉冲的持续时间内持续，不受重复刺激的影响。在比目鱼肌中，大约60%的纤维维持第一次诱发反应，其余的纤维是短暂的。瞬变反应达到峰值，然后是超极化。重复刺激不可逆转地将比目鱼肌纤维的持续性反应转变为一过性反应。当生理盐水中的钙被镁(10 MM)或钴(5 MM)取代，或加入镉(0.1-1.0 mM)或硝苯地平(5-6微米)时，反应被阻断。河豚毒素不影响这些反应。这些结果有力地表明，钙是反应过程中电流的主要载体。硝苯地平阻断钙反应和随后的超极化，提示后者是由于钙依赖钾电导的激活所致。
Slow action potentials were evoked in twitch fibres of rat extensor digitorum longus (e.d.l.) and soleus muscles after drastically reducing the Cl and K conductances of the muscle fibres. Cl conductance was eliminated by exposing the muscles to a Cl‐free saline in which methanesulphonate replaced Cl. K conductance was reduced by adding tetraethylammonium (TEA) and 3,4‐diaminopyridine (3,4‐DAP) to the Cl‐free saline or by overnight incubation of the muscles in a saline containing Cs and TEA. The delayed rectifier was markedly blocked by TEA and 3,4‐DAP. In contrast, the inward rectifier was blocked only by TEA. Depolarization with pulses of increasing amplitude triggered slow responses which had a threshold of ‐30 to ‐10 mV and a peak amplitude of 50‐60 mV. In e.d.l. muscles the time course of the response was sustained for the duration of the pulses and was not affected by repeated stimulation. In soleus muscles the first evoked response was sustained in about 60% of the fibres and transient in the rest. Transient responses reached a peak amplitude and were followed by a hyperpolarization. Repeated stimulation irreversibly transformed the sustained responses of soleus fibres into transient ones. The responses were blocked when the Ca in saline was replaced by Mg (10 mM) or Co (5 mM) or by the addition of Cd (0.1‐1.0 mM) or nifedipine (5‐6 microM). Tetrodotoxin did not affect the responses. These results strongly suggest that Ca is the main carrier of current during the response. Nifedipine blocked both the Ca response and the subsequent hyperpolarization, suggesting that the latter is due to the activation of a Ca‐dependent K conductance.