Goto M, Hyodo T, Ikeda K
Jpn J Physiol. 1983;33(5):837-54. doi: 10.2170/jjphysiol.33.837.
Properties of Ca-dependent outward current were studied in bullfrog atrial muscle using double sucrose-gap techniques. Decreasing [Ca]o inhibited the instantaneous outward current (Ik1) and inward background current (Ib), and the reverse was noted with increases in [Ca]o. When gk1 was blocked with 0.3 mM Ba, there were no such effects. In the presence of Ba and TTX (1.5 X 10(-6)M), 3 mM Co abolished the slow inward current (Isi) and depressed the delayed outward current (Iout). The depression was confined to the voltage range of activation of Isi. Similar results were obtained by replacement of [Ca]o with Co in concentration of equal surface charge effects. Contrarily, isoproterenol (10(-7) M) increased the Isi and Iout at the same voltage range. The activation of Iout became more rapid in the presence of isoproterenol but slowed with Co. In the presence of Ba, TTX, and Co, Ca-free EGTA (approximately 0.3 mM) Ringer further depressed the Iout, eliminating any remaining tension response. The depression, however, was more extensive, the stronger the depolarization. The activation of Iout was markedly retarded and amplitude of the fully activated Iout diminished, yet the deactivation became more rapid. Thus, the Ca-sensitive outward current was classified into 1) Ca-linked Ik1, 2) Isi-dependent Iout, and 3) Isi-independent but [Ca]o-related Iout.
运用双蔗糖间隙技术研究了牛蛙心房肌中钙依赖性外向电流的特性。降低细胞外钙浓度（[Ca]o）可抑制瞬时外向电流（Ik1）和内向背景电流（Ib），而升高[Ca]o则会出现相反的情况。当用0.3 mM钡阻断gk1时，未观察到此类效应。在钡和河豚毒素（TTX，1.5×10⁻⁶ M）存在的情况下，3 mM钴可消除慢内向电流（Isi）并抑制延迟外向电流（Iout）。这种抑制作用局限于Isi激活的电压范围。通过用具有相同表面电荷效应浓度的钴替代[Ca]o，也获得了类似的结果。相反，异丙肾上腺素（10⁻⁷ M）在相同电压范围内增加了Isi和Iout。在异丙肾上腺素存在的情况下，Iout的激活变得更快，但在钴存在时则减慢。在钡、TTX和钴存在的情况下，无钙的乙二胺四乙酸（EGTA，约0.3 mM）林格液进一步抑制了Iout，消除了任何剩余的张力反应。然而，抑制作用在更强的去极化时更为广泛。Iout的激活明显延迟，完全激活的Iout幅度减小，但失活变得更快。因此，钙敏感外向电流可分为：1）钙相关的Ik1，2）依赖于Isi的Iout，以及3）不依赖于Isi但与[Ca]o相关的Iout。
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