BLOCKING EFFECTS OF BARIUM AND HYDROGEN-IONS ON POTASSIUM CURRENT DURING ANOMALOUS RECTIFICATION IN STARFISH EGG
BLOCKING EFFECTS OF BARIUM AND HYDROGEN-IONS ON POTASSIUM CURRENT DURING ANOMALOUS RECTIFICATION IN STARFISH EGG
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DOI：
10.1113/jphysiol.1978.sp012338
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发表时间：
1978-01-01
影响因子：
5.5
通讯作者：
PATLAK, J
中科院分区：
文献类型：
--
作者：
HAGIWARA, S;MIYAZAKI, S;PATLAK, J
用电压钳技术研究了在海星巨型卵膜异常整流过程中，Ca~(2+)和H~+对内向K电流的阻断作用。低浓度(10-100µm)的外加Ba2+对内向K电流有抑制作用，抑制程度可用常规双分子吸附等温式描述，K/(K+[Ba2+]o)K为表观解离常数。离解常数K随膜电位V变得更负而减小，并可用K(V)=K(0)exp(zmuFV/RT)来表示，其中K(0)是V=0时的K，z是阻断离子的电荷，和MU。是Ba2+阻断膜电位依赖性的一个参数。.MU的值。范围在0.64到0.68之间。在膜电位突变时，Ba2+的阻断效应遵循一级动力学变化，正向速率常数是膜电位依赖的，而后向常数是不依赖于电位的。在异常整流过程中，Ba2+的阻断作用不依赖K通道的激活。Ba2+的阻断作用仅依赖于V，而在反常整流过程中K通道的激活依赖于V-VK。在这些方面，Ba2+的作用相当于在反常整流中引入失活。只有在浓度高得多的情况下(约10-20 mM)，锶和钙离子才表现出很小但可观察到的阻断效应。当外加pH降至6.0时，内向钾电流被抑制。H+的封闭作用不表现出明显的潜在依赖性。浓度依赖关系表明，三个H+同时滴定每个通道的酸性基团(pK=5.3-5.4)。根据K通道异常整流的分子模型和K通道失活的可能机制，讨论了这些结果的意义。
The blocking effects of Ba+ and H+ on the inward K current during anomalous rectification of the giant egg membrane of the starfish Mediaster aequalis, were studied using voltage clamp techniques. External Ba2+ at a low concentration (10-100 .mu.M) suppresses the inward K current; the extent of suppression, expressed as the ratio of currents with and without Ba2+, can be described by a conventional bimolecular adsorption isotherm, K/(K + [Ba2+]o) K being an apparent dissociation constant. The dissociation constant, K, decreases as the membrane potential V becomes more negative and can be expressed by K(V) = K(0) exp (z.mu.FV/RT) where K(0) is the K at V = 0, z is the charge of the blocking ion, and .mu. is a parameter for the membrane potential dependence of Ba2+ blockage. The value of .mu. ranges between 0.64 and 0.68. Upon a sudden change in membrane potential the change in the blocking effect of Ba2+ follows 1st order kinetics; the forward rate constant is membrane-potential-dependent whereas the backward constant is potential-independent. The blocking effect of Ba2+ appears independent of K channels activation during anomalous rectification. The blocking effect of Ba2+ depends on V alone, in contrast to the activation of the K channel during anomalous rectification which depends on V-VK. In these respects, the effect of Ba2+ is equivalent to the introduction of inactivation into the anomalous rectification. Sr2+ and Ca2+ show small but observable blocking effects only at much higher concentrations (about 10-20 mM). The inward K current is suppressed when the external pH is reduced below 6.0. The blocking effect of H+ shows no significant potential dependence. The concentration dependence suggests that three H+ simultaneously titrate the acidic groups of each channel (pK = 5.3-5.4). The implications of these results are discussed in terms of molecular models of the K channel of anomalous rectification and possible mechanisms of K channel inactivation.