Ikehara T, Yamaguchi H, Hosokawa K, Takahashi A, Miyamoto H
Department of Physiology, School of Medicine, University of Tokushima, Japan.
J Membr Biol. 1993 Mar;132(2):115-24. doi: 10.1007/BF00239001.
The effects of intracellular K+ and Na+ (K+c, Na+c) on the Na+, K+, Cl- cotransport pathway of HeLa cells were studied by measuring ouabain-insensitive, furosemide-sensitive Rb+ influx (JRb) at various intracellular concentrations of K+ and Na+ ([K+]c, [Na+]c). When [K+]c was increased and [Na+]c was decreased, keeping the sums of their concentrations almost constant, JRb as a function of the extracellular Rb+ or Na+ concentration ([Rb+]e, [Na+]e) was stimulated. However, the apparent K0.5 for Rb+e or Na+e remained unchanged and the ratio of the apparent K0.5 for K+c and the apparent Ki for Na+c was larger than 1. When JRb was increased by hypertonicity by addition of 200 mM mannitol, the apparent maximum JRb increased without change in the apparent K0.5 for Rb+e. These results show that K+c stimulates and Na+c inhibits JRb, without change in the affinities of the pathway for Rb+e and Na+e. The affinity for K+c is slightly lower than that for Na+c. Hypertonicity enhances JRb without any change in the affinity for Rb+e. We derived a kinetic equation for JRb with respect to K+c and Na+c and proposed a general and a special model of the pathway. The special model suggests that, in HeLa cells, JRb takes place when Rb+e binds to the external K+ binding site of the pathway after the binding of K+c to the internal regulatory site.
通过在不同细胞内钾离子和钠离子浓度（[K⁺]c、[Na⁺]c）下测量哇巴因不敏感、呋塞米敏感的铷离子内流（JRb），研究了细胞内钾离子和钠离子（K⁺c、Na⁺c）对HeLa细胞钠钾氯协同转运途径的影响。当[K⁺]c升高而[Na⁺]c降低，同时保持它们浓度之和几乎恒定时，作为细胞外铷离子或钠离子浓度（[Rb⁺]e、[Na⁺]e）函数的JRb受到刺激。然而，Rb⁺e或Na⁺e的表观K0.5保持不变，并且K⁺c的表观K0.5与Na⁺c的表观Ki之比大于1。当通过添加200 mM甘露醇使细胞外液渗透压升高而使JRb增加时，表观最大JRb增加，而Rb⁺e的表观K0.5不变。这些结果表明，K⁺c刺激而Na⁺c抑制JRb，同时该途径对Rb⁺e和Na⁺e的亲和力不变。对K⁺c的亲和力略低于对Na⁺c的亲和力。高渗增强JRb，而对Rb⁺e的亲和力没有任何变化。我们推导了关于JRb相对于K⁺c和Na⁺c的动力学方程，并提出了该途径的一般模型和特殊模型。特殊模型表明，在HeLa细胞中，JRb发生在K⁺c与内部调节位点结合后，Rb⁺e与该途径的外部钾离子结合位点结合时。
