Preisig P A, Rector F C
Department of Physiological Nursing, University of California, San Francisco 94143-0532.
Am J Physiol. 1988 Sep;255(3 Pt 2):F461-5. doi: 10.1152/ajprenal.1988.255.3.F461.
We recently showed that, in the presence of physiological sodium concentrations, 4.3 mM luminal amiloride inhibits 90% of apical membrane Na+-H+ antiporter activity in the in vivo microperfused rat proximal convoluted tubule. In the present studies we examined the effect of 4.3 mM luminal amiloride on transepithelial NaCl absorption from a high-chloride, low-bicarbonate perfusate, simulating the tubular fluid of the late proximal tubule. Both chloride and volume absorption were inhibited approximately 44%, consistent with inhibition of most of transcellular NaCl absorption, and suggestive of parallel Na+-H+ and Cl(-)-base exchange as the mechanism of NaCl uptake across the apical membrane. Methazolamide (10(-4) M), a potent inhibitor of renal carbonic anhydrase, had no significant effect on either volume or chloride absorption, suggesting that a carbonic anhydrase-independent mechanism is at least partially involved in chloride absorption. Hydrochlorothiazide (1 mM), an inhibitor of electroneutral NaCl cotransport in tight epithelia, did not significantly affect either volume or chloride absorption. Thus these studies suggest that, in the rat, the mechanism of apical membrane electroneutral NaCl uptake is Na+-H+ and Cl- -base exchange.
我们最近发现，在生理钠浓度存在的情况下，4.3 mM的管腔阿米洛利可抑制体内微灌注大鼠近端曲管顶膜钠氢交换体活性的90%。在本研究中，我们研究了4.3 mM管腔阿米洛利对高氯、低碳酸氢盐灌注液中跨上皮氯化钠吸收的影响，模拟近端小管后期的小管液。氯和容量吸收均被抑制约44%，这与大多数跨细胞氯化钠吸收的抑制一致，并提示平行的钠氢和氯碱交换是氯化钠通过顶膜摄取的机制。甲醋唑胺（10^(-4) M），一种强力的肾碳酸酐酶抑制剂，对容量或氯吸收均无显著影响，表明一种不依赖碳酸酐酶的机制至少部分参与了氯吸收。氢氯噻嗪（1 mM），一种紧密上皮中电中性氯化钠共转运的抑制剂，对容量或氯吸收均无显著影响。因此，这些研究表明，在大鼠中，顶膜电中性氯化钠摄取的机制是钠氢和氯碱交换。
