猪胃（H⁺，K⁺）-ATP酶对Rb⁺的被动转运

Passive transport of Rb+ by hog gastric (H+,K+)-ATPase.

作者信息

Soumarmon A, Rangachari P K, Lewin M J

出版信息

J Biol Chem. 1984 Oct 10;259(19):11861-7.

Abstract

Gastric vesicles enriched in (H+,K+)-ATPase were prepared from hog fundic mucosa and studied for their ability to transport K+ using 86Rb+ as tracer. In the absence of ATP, the vesicles elicited a rapid uptake of 86Rb+ (t 1/2 = 45 +/- 9 s at 30 degrees C) which accounted for both transport and binding. Transport was osmotically sensitive and was the fastest phase. It was not limited by anion permeability (C1- was equivalent to SO2-4) but rather by availability of either H+ or K+ as intravesicular countercation suggesting a Rb+-K+ or a Rb+-H+ exchange. Selectivity was K+ greater than Rb+ greater than Cs+ much greater than Na+,Li+. The capacity of vesicles which catalyzed the fast transport of K+ was 83 +/- 4% of maximal vesicular capacity of the fraction. Addition of ATP decreased both rate and extent of 86Rb+ uptake (by 62 and 43%, respectively with 1 mM ATP) with an apparent Ki of 30 microM. Such an effect was not seen on 22Na+ transport. ATP inhibition of transport did not require the presence of Mg2+, and inhibition was also produced by ADP even in the presence of myokinase inhibitor. On the other hand, 86Rb+ uptake was as strongly inhibited by 200 microM vanadate in the presence of Mg2+. Efflux studies suggested that ATP inhibition was originally due to a decrease of vesicular influx with little or no modification of efflux. Since ATP, ADP, and vanadate are known modulators of the (H+,K+)-ATPase, we propose that, in the absence of ATP, (H+,K+)-ATPase passively exchanges K+ for K+ or H+ and that ATP, ADP, and vanadate regulate this exchange.

摘要

从猪胃底黏膜制备富含（H⁺，K⁺）-ATP酶的胃小泡，并以⁸⁶Rb⁺作为示踪剂研究其转运K⁺的能力。在无ATP的情况下，胃小泡引起⁸⁶Rb⁺的快速摄取（30℃时t₁/₂ = 45±9秒），这包括转运和结合。转运对渗透压敏感且是最快的阶段。它不受阴离子通透性的限制（Cl⁻相当于SO₄²⁻），而是受作为泡内抗衡阳离子的H⁺或K⁺的可用性限制，提示存在Rb⁺-K⁺或Rb⁺-H⁺交换。选择性为K⁺＞Rb⁺＞Cs⁺＞＞Na⁺，Li⁺。催化K⁺快速转运的胃小泡的能力为该组分最大胃小泡能力的83±4%。添加ATP降低了⁸⁶Rb⁺摄取的速率和程度（1 mM ATP时分别降低62%和43%），表观Ki为30 μM。在²²Na⁺转运中未观察到这种效应。ATP对转运的抑制不需要Mg²⁺的存在，即使在有肌酸激酶抑制剂的情况下，ADP也能产生抑制作用。另一方面，在有Mg²⁺存在时，200 μM钒酸盐对⁸⁶Rb⁺摄取的抑制作用同样强烈。流出研究表明，ATP抑制最初是由于泡内流入减少，流出几乎没有改变或没有改变。由于ATP、ADP和钒酸盐是已知的（H⁺，K⁺）-ATP酶的调节剂，我们提出，在无ATP的情况下，（H⁺，K⁺）-ATP酶被动地将K⁺与K⁺或H⁺进行交换，并且ATP、ADP和钒酸盐调节这种交换。