Cougnon M, Bouyer P, Planelles G, Jaisser F
Institut National de la Santé et de la Recherche Médicale, U. 467, Faculté de Médecine Necker, Université Paris V, F-75015 Paris, France.
Proc Natl Acad Sci U S A. 1998 May 26;95(11):6516-20. doi: 10.1073/pnas.95.11.6516.
We previously have demonstrated that the colonic P-ATPase alpha subunit cDNA encodes an H,K-ATPase when expressed in Xenopus laevis oocytes. Besides its high level of amino acid homology (75%) with the Na,K-ATPase, the colonic H,K-ATPase also shares a common pharmacological profile with Na,K-ATPase, because both are ouabain-sensitive and Sch 28080-insensitive. These features raise the possibility that an unrecognized property of the colonic H, K-ATPase would be Na+ translocation. To test this hypothesis, ion-selective microelectrodes were used to measure the intracellular Na+ activity of X. laevis oocytes expressing various combinations of P-ATPase subunits. The results show that expression in oocytes of the colonic H,K-ATPase affects intracellular Na+ homeostasis in a way similar to the expression of the Bufo marinus Na,K-ATPase; intracellular Na+ activity is lower in oocytes expressing the colonic H,K-ATPase or the B. marinus Na,K-ATPase than in oocytes expressing the gastric H,K-ATPase or a beta subunit alone. In oocytes expressing the colonic H,K-ATPase, the decrease in intracellular Na+ activity persists when diffusive Na+ influx is enhanced by functional expression of the amiloride-sensitive epithelial Na+ channel, suggesting that the decrease is related to increased active Na+ efflux. The Na+ decrease depends on the presence of K+ in the external medium and is inhibited by 2 mM ouabain, a concentration that inhibits the colonic H,K-ATPase. These data are consistent with the hypothesis that the colonic H,K-ATPase may transport Na+, acting as an (Na,H),K-ATPase. Despite its molecular and functional characterization, the physiological role of the colonic (Na,H),K-ATPase in colonic and renal ion homeostasis remains to be elucidated.
我们之前已经证明,结肠P - ATP酶α亚基cDNA在非洲爪蟾卵母细胞中表达时编码一种H,K - ATP酶。除了与Na,K - ATP酶具有高度的氨基酸同源性(75%)外,结肠H,K - ATP酶还与Na,K - ATP酶具有共同的药理学特征,因为两者都对哇巴因敏感而对Sch 28080不敏感。这些特征增加了结肠H,K - ATP酶具有未被认识的Na⁺转运特性的可能性。为了验证这一假设,使用离子选择性微电极测量表达P - ATP酶亚基各种组合的非洲爪蟾卵母细胞的细胞内Na⁺活性。结果表明,结肠H,K - ATP酶在卵母细胞中的表达以类似于海蟾蜍Na,K - ATP酶表达的方式影响细胞内Na⁺稳态;表达结肠H,K - ATP酶或海蟾蜍Na,K - ATP酶的卵母细胞中的细胞内Na⁺活性低于表达胃H,K - ATP酶或单独表达β亚基的卵母细胞。在表达结肠H,K - ATP酶的卵母细胞中,当通过氨氯地平敏感的上皮Na⁺通道的功能性表达增强扩散性Na⁺内流时,细胞内Na⁺活性的降低仍然存在,这表明这种降低与活性Na⁺外流增加有关。Na⁺的降低取决于细胞外培养基中K⁺的存在,并被2 mM哇巴因抑制,该浓度可抑制结肠H,K - ATP酶。这些数据与结肠H,K - ATP酶可能作为(Na,H),K - ATP酶转运Na⁺的假设一致。尽管对结肠(Na,H),K - ATP酶进行了分子和功能表征,但其在结肠和肾脏离子稳态中的生理作用仍有待阐明。