Garty H, Civan E D, Civan M M
J Membr Biol. 1985;87(1):67-75. doi: 10.1007/BF01870700.
We have examined the effect of internal and external pH on Na+ transport across toad bladder membrane vesicles. Vesicles prepared and assayed with a recently modified procedure (Garty & Asher, 1985) exhibit large, rheogenic, amiloride-sensitive fluxes. Of the total 22Na uptake measured 0.5-2.0 min after introducing tracer, 80 +/- 4% (mean +/- SE, n = 9) is blocked by the diuretic with a KI of 2 X 10(-8) M. Thus, this amiloride-sensitive flux is mediated by the apical sodium-selective channels. Varying the internal (cytosolic) pH over the physiologic range 7.0-8.0 had no effect on sodium transport; this result suggests that variation of intracellular pH in vivo has no direct apical effect on modulating sodium uptake. On the other hand, 22Na was directly and monotonically dependent on external pH. External acidification also reduced the amiloride-sensitive efflux across the walls of the vesicles. This inhibition of 22Na efflux was noted at external Na+ concentrations of both 0.2 microM and 53 mM. These results are different from those reported with whole toad bladder. A number of possible bases for these differences are considered and discussed. We suggest that the natriferic response induced by mucosal acidification of whole toad urinary bladder appears to operate indirectly through one or more factors, presumably cytosolic, present in whole cells and absent from the vesicles.
我们研究了内部和外部pH值对钠离子跨蟾蜍膀胱膜囊泡转运的影响。用最近改进的方法（加蒂和阿舍，1985年）制备并检测的囊泡表现出大量、生电的、对氨氯地平敏感的通量。在引入示踪剂后0.5 - 2.0分钟测量的总22Na摄取量中，80±4%（平均值±标准误，n = 9）被该利尿剂阻断，其抑制常数为2×10(-8)M。因此，这种对氨氯地平敏感的通量是由顶端钠选择性通道介导的。在生理范围7.0 - 8.0内改变内部（胞质）pH值对钠转运没有影响；这一结果表明，体内细胞内pH值的变化对调节钠摄取没有直接的顶端效应。另一方面，22Na直接且单调地依赖于外部pH值。外部酸化也降低了跨囊泡壁的对氨氯地平敏感的外流。在外部Na+浓度为0.2微摩尔和53毫摩尔时均观察到对22Na外流的这种抑制作用。这些结果与用完整蟾蜍膀胱报道的结果不同。我们考虑并讨论了造成这些差异的一些可能原因。我们认为，完整蟾蜍膀胱黏膜酸化诱导的排钠反应似乎是通过一个或多个因素间接起作用的，这些因素大概存在于完整细胞的胞质中，而囊泡中不存在。
