近端小管中依赖钠的氢离子外流：钠-氢可逆交换的证据。

Na+-dependent H+ efflux from proximal tubule: evidence for reversible Na+-H+ exchange.

作者信息

Schwartz G J

出版信息

Am J Physiol. 1981 Oct;241(4):F380-5. doi: 10.1152/ajprenal.1981.241.4.F380.

DOI:10.1152/ajprenal.1981.241.4.F380

Abstract

Removal of Na+ or addition of ouabain inhibits HCO3(-) and Na+ absorption in rabbit proximal tubule, a finding suggestive of Na+-H+ coupling. However, inhibition of Na+ transport might decrease H+ secretion by reducing energy metabolism rather than by inhibiting Na+-H+ exchange directly. H+ disappearance from the luminal fluid, which depends on direction and magnitude of Na+ gradient, should be a function of cell Na+, independent of cellular metabolism. If cell Na+ is increased by ouabain, H+ disappearance should increase; when cell Na+ is reduced by Na+ removal, less H+ should level the lumen for a given pH difference. Superficial early proximal convoluted tubules were dissected from rabbit kidney and perfused rapidly in vitro with CO2(-) and HCO3(-)-free solutions (pH 6.45). The bath resembled perfusate except that the pH was 7.4 and contained 6 g/dl of albumin. H+ efflux was calculated from the difference in pH between perfused and collected fluid, flow rate, and buffer capacity of the perfusate. When 145 mM Na+ was present in perfusate and bath, H+ efflux was 5.3 +/- 0.4 pmol . cm-1 . s-1 and increased by 39 +/- 16% when ouabain was added to the bath. Replacement of Na+ by choline or Li+ caused a 44 +/- 7% decrease in H+ efflux. Removal of luminal organic solutes markedly reduced H+ efflux; however, it was still enhanced by addition of ouabain to the bath. Even in the absence of Na+ or luminal organic solutes, a substantial apparent H+ leak permeability exists. Addition of 10(-4) M amiloride to a 10 mM Na+ medium caused a 34 +/- 6% reduction in H+ efflux. The results indicate that H+ transport in the proximal tubule is mediated, at least in part, by a reversible Na+-H+ exchanger driven by the difference between H+ and Na+ gradients.

摘要

去除Na⁺或添加哇巴因会抑制兔近端小管中HCO₃⁻和Na⁺的重吸收，这一发现提示存在Na⁺-H⁺偶联。然而，抑制Na⁺转运可能是通过降低能量代谢而非直接抑制Na⁺-H⁺交换来减少H⁺分泌。管腔液中H⁺的消失取决于Na⁺梯度的方向和大小，应该是细胞内Na⁺的函数，与细胞代谢无关。如果用哇巴因使细胞内Na⁺增加，H⁺的消失应该增加；当通过去除Na⁺使细胞内Na⁺减少时，对于给定的pH差值，管腔内的H⁺水平应该降低。从兔肾中分离出浅表早期近端曲小管，并在体外迅速用不含CO₂⁻和HCO₃⁻的溶液（pH 6.45）进行灌注。浴液类似于灌注液，只是pH为7.4且含有6 g/dl的白蛋白。根据灌注液和收集液之间的pH差值、流速以及灌注液的缓冲能力来计算H⁺外流。当灌注液和浴液中存在145 mM Na⁺时，H⁺外流为5.3±0.4 pmol·cm⁻¹·s⁻¹，当向浴液中添加哇巴因时，H⁺外流增加39±16%。用胆碱或Li⁺替代Na⁺导致H⁺外流减少44±7%。去除管腔有机溶质可显著降低H⁺外流；然而，向浴液中添加哇巴因仍可增强H⁺外流。即使在没有Na⁺或管腔有机溶质的情况下，也存在大量明显的H⁺渗漏通透性。向10 mM Na⁺培养基中添加10⁻⁴ M氨氯吡脒可使H⁺外流减少34±6%。结果表明，近端小管中的H⁺转运至少部分是由由H⁺和Na⁺梯度差异驱动的可逆性Na⁺-H⁺交换体介导的。