Rajendran V M, Oesterlin M, Binder H J
Department of Internal Medicine, Yale University School of Medicine, New Haven, Connecticut 06510.
J Clin Invest. 1991 Oct;88(4):1379-85. doi: 10.1172/JCI115444.
This study sought to characterize the mechanism of Na transport across basolateral membrane vesicles of rat distal colon. Both an outward proton gradient and an inward bicarbonate gradient stimulated 22Na uptake. Proton gradient-stimulated 22Na uptake was activated severalfold by the additional presence of an inward bicarbonate gradient, and bicarbonate gradient-stimulated 22Na uptake was significantly enhanced by an imposed intravesicular membrane positive potential. 0.1 mM amiloride inhibited both proton gradient- and bicarbonate gradient-stimulated 22Na uptake by 80 and 95%, respectively, while 1 mM 4,4'-diisothiocyanatostilbene-2,2'-disulfonic acid (DIDS) inhibited both proton gradient- and bicarbonate gradient-stimulated 22Na uptake by 40 and 80%, respectively. Both proton gradient- and bicarbonate gradient-stimulated 22Na uptake saturated as a function of increasing Na concentration: the apparent kinetic constants (Km) for Na for the DIDS-insensitive component of proton gradient-stimulated 22Na uptake was 46.4 mM, while the DIDS-sensitive component of proton gradient- and bicarbonate gradient-stimulated 22Na uptake had Km for Na of 8.1 and 6.4 mM, respectively. Amiloride inhibited both DIDS-insensitive proton gradient- and bicarbonate gradient-stimulated 22Na uptake with an inhibitory constant (Ki) of approximately 35 and 1 microM, respectively. We conclude from these results that proton gradient-stimulated 22Na uptake represents both DIDS-insensitive Na-H exchange and DIDS-sensitive electrogenic Na-OH cotransport, and that the DIDS-sensitive component of proton gradient-stimulated 22Na uptake and bicarbonate gradient-stimulated 22Na uptake may represent the same electrogenic Na-anion cotransport process.
本研究旨在阐明大鼠远端结肠基底外侧膜囊泡跨膜转运钠的机制。外向质子梯度和内向碳酸氢根梯度均能刺激22Na摄取。质子梯度刺激的22Na摄取在额外存在内向碳酸氢根梯度时可被激活数倍，而碳酸氢根梯度刺激的22Na摄取在施加囊泡内正膜电位时显著增强。0.1 mM氨氯吡咪分别抑制质子梯度和碳酸氢根梯度刺激的22Na摄取达80%和95%，而1 mM 4,4'-二异硫氰基芪-2,2'-二磺酸（DIDS）分别抑制质子梯度和碳酸氢根梯度刺激的22Na摄取达40%和80%。质子梯度和碳酸氢根梯度刺激的22Na摄取均随钠浓度增加而饱和：质子梯度刺激的22Na摄取中对DIDS不敏感部分的钠表观动力学常数（Km）为46.4 mM，而质子梯度和碳酸氢根梯度刺激的22Na摄取中对DIDS敏感部分的钠Km分别为8.1 mM和6.4 mM。氨氯吡咪抑制对DIDS不敏感的质子梯度和碳酸氢根梯度刺激的22Na摄取，抑制常数（Ki）分别约为35 μM和1 μM。从这些结果我们得出结论，质子梯度刺激的22Na摄取代表对DIDS不敏感的钠-氢交换和对DIDS敏感的电中性钠-氢氧根共转运，且质子梯度刺激的22Na摄取和碳酸氢根梯度刺激的22Na摄取中对DIDS敏感部分可能代表相同的电中性钠-阴离子共转运过程。
