ANOXIC SUPPRESSION OF NA+-K+-ATPASE AND CONSTANT MEMBRANE-POTENTIAL IN HEPATOCYTES - SUPPORT FOR CHANNEL ARREST
ANOXIC SUPPRESSION OF NA+-K+-ATPASE AND CONSTANT MEMBRANE-POTENTIAL IN HEPATOCYTES - SUPPORT FOR CHANNEL ARREST
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DOI：
10.1152/ajpregu.1993.265.5.r1020
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发表时间：
1993-11-01
影响因子：
--
通讯作者：
HOCHACHKA, PW
中科院分区：
文献类型：
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作者：
BUCK, LT;HOCHACHKA, PW
通过Na+-K+- atp酶维持跨质膜的离子梯度已被证明利用了细胞总能量需求的很大一部分。考虑到离子梯度对细胞功能的重要性，以及赤蠵龟及其肝细胞对缺氧的耐受性，我们有兴趣确定在对缺氧的反应中，1)离子梯度是否维持，2)质膜Na+-K+- atp酶的活性是否改变以帮助维持离子梯度。从常氧肝细胞悬液中测定了瓦阿因抑制的Rb-86+摄取（Na+-K+-ATP酶活性的测量），ATP利用率为19.1 μ mol ATP。g细胞-1 - h-1或28%的总常氧细胞ATP周转。在缺氧孵育的反应中，泵的活性下降了75%至4.8 μ mol ATP。g细胞-1.h-1，这占总缺氧ATP周转量的74%。目前，尚不清楚观察到的Na+-K+- atp酶活性的降低是否受1)变构修饰，2)膜内吞作用或3)Na+内流减少的调节。在缺氧时，利用Cl-36-的分布测量了质膜电位，与正常情况下的测量值无显著差异，分别为-30.6 +/- 3.9 mV和-31.3 +/- 5.8 mV。因此，缺氧时质膜离子梯度得以维持，由于NA+-K+- atp酶活性降低，离子的流入也必然减少。Na+-K+- atp酶活性的降低和对缺氧反应的恒定膜电位的结合支持了通道阻滞的概念。
The maintenance of ion gradients across the plasma membrane by the Na+-K+-ATPase has been shown to utilize a large fraction of the total cellular energy demand. In view of the importance of ion gradients to cellular function, and the remarkable anoxia tolerance of Chrysemys picta bellii (western painted turtle) and hepatocytes isolated from this species, it was of interest to determine if in response to anoxia 1) ion gradients were maintained and 2) if the activity of the plasma membrane Na+-K+-ATPase changed to aid in ion gradient maintenance. From normoxic hepatocyte suspensions the ouabain-inhibitable Rb-86+ uptake (a measure of Na+-K+-ATPase activity) was determined, and the rate of ATP utilization was 19.1 mumol ATP.g cells-1.h-1 or 28% of the total normoxic cellular ATP turnover. In response to anoxic incubation the activity of the pump decreased by 75% to 4.8 mumol ATP.g cells-1.h-1 and this comprised 74% of the total anoxic ATP turnover. Presently, it is not known whether the observed reduction in Na+-K+-ATPase activity is regulated by 1) allosteric modification, 2) endocytosis from the membrane, or 3) reduced Na+ influx. Plasma membrane potential was measured during anoxia, using the distribution of Cl-36-, and was not significantly different from the normoxic measurement, -30.6 +/- 3.9 and -31.3 +/- 5.8 mV, respectively. Therefore, the plasma membrane ion gradient is maintained during anoxia, and since the activity of the NA+-K+-ATPase decreases, the influx of ions must also decrease. The combination of a decrease in Na+-K+-ATPase activity and a constant membrane potential in response to anoxia supports the channel arrest concept.