Reuss L, Cheung L Y, Grady T P
J Membr Biol. 1981 Apr 30;59(3):211-24. doi: 10.1007/BF01875426.
Conventional microelectrode techniques were combined with unilateral mucosal ionic substitutions to determine the effects of luminal pH and luminal alkali-earth cation concentrations on apical membrane cation permeability in Necturus gallbladder epithelium. Acidification of the mucosal solution caused reversible depolarization of both cell membranes and increase of transepithelial resistance. Low pH media also caused: (a) reduction of the apical membrane depolarization induced by high K, and (b) increase of the apical membrane hyperpolarization produced by Na replacement with Li or N-Methyl-D-glucamine. These results, in conjunction with estimates of cell membrane conductances, indicate that acidification of the luminal solution produces a reduction of apical membrane K permeability (PK). Addition of alkali earth cations (Mg2+, Ca2+, Sr2+, or Ba2+) produced cell membrane depolarization, increase of relative resistance of the luminal membrane and reduction of the apical membrane potential change produced by a high-K mucosal medium. These results, as those produced by low pH, can be explained by a reduction of apical membrane PK. The effects of Ba2+ on membrane potential and relative apical membrane PK were larger than those of all other four cations at all concentrations tested (1-10 mM). The effect of Sr2+ was significantly larger than those of Mg2+ and Ca2+ at 10 mM, but not different at 5 mM. The reduction of PK produced by mucosal acidification appears to be mediated by: (a) nonspecific titration of membrane fixed negative charges, and (b) an effect of luminal proton activity on the apical K channel. Divalent cations reduce apical membrane PK probably by screening negative surface charges. The larger magnitude of the effects of Ba2+ and Sr2+ can be explained by binding to membrane sites, in the surface or in the K channel, in addition to their screening effect. We suggest that the action of luminal pH on K secretion in some segments of the renal tubule could be mediated in part by this pH-dependent K permeability of the luminal membrane.
传统微电极技术与单侧黏膜离子置换相结合，以确定管腔pH值和管腔碱土金属阳离子浓度对美西螈胆囊上皮细胞顶端膜阳离子通透性的影响。黏膜溶液酸化导致细胞膜可逆性去极化，并使跨上皮电阻增加。低pH值介质还导致：（a）高钾诱导的顶端膜去极化减弱，以及（b）用锂或N-甲基-D-葡糖胺替代钠所产生的顶端膜超极化增强。这些结果与细胞膜电导估计值相结合，表明管腔溶液酸化导致顶端膜钾通透性（PK）降低。添加碱土金属阳离子（Mg2+、Ca2+、Sr2+或Ba2+）导致细胞膜去极化、管腔膜相对电阻增加以及高钾黏膜介质所产生的顶端膜电位变化减小。这些结果与低pH值所产生的结果一样，可通过顶端膜PK降低来解释。在所有测试浓度（1 - 10 mM）下，Ba2+对膜电位和顶端膜相对PK的影响均大于其他四种阳离子。在10 mM时，Sr2+的影响显著大于Mg2+和Ca2+，但在5 mM时无差异。黏膜酸化所导致的PK降低似乎是由：（a）膜固定负电荷的非特异性滴定，以及（b）管腔质子活性对顶端钾通道的影响介导的。二价阳离子可能通过屏蔽表面负电荷来降低顶端膜PK。Ba2+和Sr2+作用的更大强度除了其屏蔽作用外，还可通过与表面或钾通道中的膜位点结合来解释。我们认为，管腔pH值对肾小管某些节段钾分泌的作用可能部分由管腔膜这种pH依赖性钾通透性介导。
