Weinman S A, Reuss L
J Gen Physiol. 1984 Jan;83(1):57-74. doi: 10.1085/jgp.83.1.57.
The role of Na+-H+ exchange in Na+ transport across the apical membrane was evaluated in Necturus gallbladder epithelium by means of intracellular Na+ activity (aNai) and 22Na+ uptake measurements. Under control conditions, complete replacement of Na+ in the mucosal solution with tetramethylammonium reduced aNai from 14.0 to 6.9 mM in 2 min (P less than 0.001). Mucosal addition of the Na+-H+ exchange inhibitor amiloride (10(-3) M) reduced aNai from 15.0 to 13.3 mM (P less than 0.001), whereas bumetanide (10(-5) and 10(-4) M) had no effect. Na+ influx across the apical membrane was studied by treating the tissues with ouabain, bathing them in Na-free solutions, and suddenly replacing the mucosal solution with an Na-containing solution. When the mucosal solution was replaced with Na-Ringer's, aNai increased at approximately 11 mM/min. This increase was inhibited by 54% by amiloride (10(-3) M, P less than 0.001) and was unaffected by bumetanide (10(-5) M). Amiloride-inhibitable Na+ fluxes across the apical membrane were also induced by the imposition of pH gradients. Na+ influx was also examined in tissues that had not been treated with ouabain. Under control conditions, 22Na+ influx from the mucosal solution into the epithelium was linear over the first 60 s and was inhibited by 40% by amiloride (10(-3) M, P less than 0.001) and by 19% by bumetanide (10(-5) M, P less than 0.025). We conclude that Na+-H+ exchange is a major pathway for Na+ entry in Necturus gallbladder, which accounts for at least half of apical Na+ influx both under transporting conditions and during exposure to ouabain. Bumetanide-inhibitable Na+ entry mechanisms may account for only a smaller fraction of Na+ influx under transporting conditions, and cannot explain influx in ouabain-treated tissues. These results support the hypothesis that NaCl entry results primarily from the operation of parallel Na+-H+ and Cl--HCO-3 exchangers, and not from a bumetanide-inhibitable NaCl cotransporter.
通过细胞内钠离子活性（aNai）和22Na+摄取量测量，评估了美洲蟾蜍胆囊上皮细胞中Na+-H+交换在钠离子跨顶端膜转运中的作用。在对照条件下，用四甲基铵完全替代黏膜溶液中的钠离子，可使aNai在2分钟内从14.0 mM降至6.9 mM（P<0.001）。黏膜添加Na+-H+交换抑制剂氨氯吡咪（10(-3) M）可使aNai从15.0 mM降至13.3 mM（P<0.001），而布美他尼（10(-5)和10(-4) M）则无作用。通过用哇巴因处理组织、将其置于无钠溶液中并突然用含钠溶液替代黏膜溶液，研究了钠离子跨顶端膜的内流情况。当用钠林格氏液替代黏膜溶液时，aNai以约11 mM/min的速度增加。氨氯吡咪（10(-3) M）可抑制这种增加的54%（P<0.001），而布美他尼（10(-5) M）则无影响。施加pH梯度也可诱导氨氯吡咪可抑制的跨顶端膜钠离子通量。还在未用哇巴因处理的组织中检测了钠离子内流。在对照条件下，从黏膜溶液进入上皮细胞的22Na+内流在最初60秒内呈线性，氨氯吡咪（10(-3) M）可抑制40%（P<0.001），布美他尼（10(-5) M）可抑制19%（P<0.025）。我们得出结论，Na+-H+交换是美洲蟾蜍胆囊中钠离子进入的主要途径，在转运条件下和暴露于哇巴因期间，它至少占顶端钠离子内流的一半。布美他尼可抑制的钠离子进入机制在转运条件下可能仅占钠离子内流的较小部分，且无法解释用哇巴因处理的组织中的内流情况。这些结果支持以下假设：NaCl的进入主要源于平行的Na+-H+和Cl--HCO-3交换体的作用，而非源于布美他尼可抑制的NaCl共转运体。
