Civan M M, Hall T A, Gupta B L
J Membr Biol. 1980 Aug 7;55(3):187-202. doi: 10.1007/BF01869460.
The bulk of the intracellular potassium in mucosal epithelial cells from toad urinary bladder has been previously reported to exchange very slowly with the serosal medium, with a half-time of some 9 hr. This observation, based on chemical analyses of mucosal cell scrapings, has been reexamined with stimultaneous diffractive and energy dispersive electron probe X-ray microanalysis. Fifty-three intracellular sites in hydrated sections and 286 sites in dehydrated sections were studied in bladders from eight toads under baseline conditions and after removal of serosal K+ for 83-133 min, with or without 10(-2) M ouabain. The baseline data confirm and extend previous examinations of the intracellular ionic composition, and provide the most direct measure of intracellular water thus far available for this tissue. Removal of serosal K+ reduced the intracellular K+ content by 20%, increased intracellular Na+ content threefold, and slightly reduced the intracellular Cl- and water contents, qualitatively consistent with published chemical analyses. The intracellular Na+ content of mucosal origin, measured by radioactive tracers and chemical analyses of cell scrapings, has been reported to be unchanged under these conditions. Simultaneous addition of ouabain and removal of external K+ produced a dramatic fall in intracellular K+ of more than 80% in a third of the cells and reduced the mean intracellular K+ content by 60%; 20% of the cells appeared to retain K+ more effectively than the bulk of the epithelial cell population. We conclude that: (i) the low rate of net exchange of intracellular K+ with the serosal bulk solution primarily reflects recycling of K+ across the basolateral membranes, (ii) radioactive tracer and chemical measurements of the intracellular Na+ pool of mucosal origin substantially understimate the total intracellular Na+ content under certain experimental conditions, and (iii) the epithelial cells display a functional heterogeneity of response to the effects of adding ouabain and withdrawing external K+.
先前有报道称，蟾蜍膀胱黏膜上皮细胞内的大部分钾与浆膜介质交换非常缓慢，半衰期约为9小时。基于对黏膜细胞刮片的化学分析得出的这一观察结果，已通过同步衍射和能量色散电子探针X射线微分析进行了重新研究。在基线条件下以及在去除浆膜钾离子83 - 133分钟后，对来自8只蟾蜍膀胱的水合切片中的53个细胞内位点和脱水切片中的286个位点进行了研究，研究过程中使用或未使用10⁻² M哇巴因。基线数据证实并扩展了先前对细胞内离子组成的研究，并提供了迄今为止该组织可获得的最直接的细胞内水分测量方法。去除浆膜钾离子使细胞内钾含量降低了20%，细胞内钠离子含量增加了三倍，并略微降低了细胞内氯离子和水分含量，这在质量上与已发表的化学分析结果一致。据报道，在这些条件下，通过放射性示踪剂和细胞刮片的化学分析测量得出的黏膜来源的细胞内钠离子含量没有变化。同时添加哇巴因并去除细胞外钾离子，导致三分之一的细胞内钾离子急剧下降超过80%，平均细胞内钾含量降低了60%；20%的细胞似乎比大多数上皮细胞群体更有效地保留了钾离子。我们得出以下结论：(i) 细胞内钾离子与浆膜大量溶液的低净交换率主要反映了钾离子跨基底外侧膜的循环，(ii) 在某些实验条件下，放射性示踪剂和化学测量得出的黏膜来源的细胞内钠离子池大大低估了细胞内总钠离子含量，(iii) 上皮细胞对添加哇巴因和去除细胞外钾离子的影响表现出功能异质性。
