Dudeja P K, Foster E S, Brasitus T A
Department of Medicine, University of Chicago, Illinois.
Am J Physiol. 1989 Oct;257(4 Pt 1):G624-32. doi: 10.1152/ajpgi.1989.257.4.G624.
The present experiments were conducted, using acridine orange and 22Na uptake techniques, to demonstrate the presence of an electroneutral Na+-H+ exchange process in rat colonic basolateral membrane vesicles. Results consistent with the existence of a distinct Na+-H+ antiporter in these vesicles include the following: 1) an outwardly directed Na+ gradient stimulated proton influx (Na+in, 100 mM; pHin 7.5/pHout 7.5) and an inwardly directed sodium gradient (Na+out, 5-50 mM; pHin 6.0/pHout 7.5) stimulated proton efflux; 2) sodium-stimulated proton influx was minimally decreased (approximately 10-25%) under voltage clamp conditions (addition of valinomycin in the presence of K+ on both sides of vesicles), indicating that Na+ for H+ exchange in these vesicles could not be explained solely on the basis of a membrane potential; 3) an outwardly directed proton gradient (pHin 5.5/pHout 7.5) stimulated 22Na uptake into these vesicles and a threefold "over-shoot" was observed; 4) 22Na uptake and sodium-stimulated proton efflux were saturable with a Km for Na+ of 5.8 +/- 0.9 and 7.0 +/- 0.3 mM, respectively; 5) amiloride (1 mM) significantly inhibited both sodium-stimulated proton efflux (approximately 69%) and 22Na uptake (approximately 89%), but other transport inhibitors (acetazolamide, 4-acetamido-4'isothiocyanostilbene-2,2'-disulfonic acid, and bumetanide) had no effect on 22Na uptake; 6) N-methylglucamine+ (a nonpermeant cation) did not affect pH gradient-stimulated 22Na uptake, whereas Li+ inhibited Na+ uptake; 7) an inwardly directed Li+ gradient stimulated proton efflux and the Km for Li+ was 12.5 +/- 1.5 mM. These findings establish the existence of an electroneutral Na+-H+ exchange mechanism in rat colonic basolateral membrane vesicles.
采用吖啶橙和22Na摄取技术进行了本实验，以证明大鼠结肠基底外侧膜囊泡中存在电中性Na+-H+交换过程。这些囊泡中存在独特的Na+-H+反向转运体的相关结果如下：1）外向性Na+梯度刺激质子内流（Na+in，100 mM；pHin 7.5/pHout 7.5），内向性钠梯度（Na+out，5 - 50 mM；pHin 6.0/pHout 7.5）刺激质子外流；2）在电压钳制条件下（囊泡两侧均存在K+时添加缬氨霉素），钠刺激的质子内流仅略有降低（约10 - 25%），这表明这些囊泡中Na+与H+的交换不能仅基于膜电位来解释；3）外向性质子梯度（pHin 5.5/pHout 7.5）刺激22Na摄取进入这些囊泡，并观察到三倍的“过冲”现象；4）22Na摄取和钠刺激的质子外流对Na+的Km分别为5.8±0.9和7.0±0.3 mM，均具有饱和性；5）氨氯地平（1 mM）显著抑制钠刺激的质子外流（约69%）和22Na摄取（约89%），但其他转运抑制剂（乙酰唑胺、4 - 乙酰氨基 - 4' - 异硫氰基芪 - 2,2' - 二磺酸和布美他尼）对22Na摄取无影响；6）N - 甲基葡糖胺 +（一种非渗透性阳离子）不影响pH梯度刺激的22Na摄取，而Li+抑制Na+摄取；7）内向性Li+梯度刺激质子外流，Li+的Km为12.5±1.5 mM。这些发现证实了大鼠结肠基底外侧膜囊泡中存在电中性Na+-H+交换机制。
