Stoddard J S, Helman S I
Am J Physiol. 1985 Nov;249(5 Pt 2):F662-71. doi: 10.1152/ajprenal.1985.249.5.F662.
An isotopic method was developed to measure the intracellular Na+ content of the transepithelial Na+ transport pool of frog skin. Isolated epithelia (no corium) were labeled with 24Na either asymmetrically, from apical (Aa) or basolateral (Ab) solutions, or symmetrically (Aab). Transport pool Na+ could be identified from the kinetics of washout of 24Na carried out in the presence of 1 mM ouabain, 100 microM amiloride, and 1 mM furosemide that served to trap cold Na+ and 24Na within the transport pool. In control epithelia, Aab averaged 64.1 neq/cm2 (13.9 mM), and maximal inhibition of apical membrane Na+ entry with 100 microM amiloride caused Aab to decrease to 24.3 neq/cm2 (5.3 mM). Ouabain caused Aab to increase markedly to 303 neq/cm2 in 30 min, whereas amiloride inhibition of apical membrane Na+ entry reduced markedly the rate of increase of Aab caused by ouabain (7.3 neq X cm-2 X min-1 in control and 1.7 neq X cm-2 X min-1 in the presence of amiloride). These data, in part, confirmed the existence of an important basolateral membrane permeability to Na+ that was measured in separate studies of the bidirectional 24Na fluxes at the basolateral membranes of the cells. Both sets of data were supportive of the idea that a significant Na+ recycling exists at the basolateral membranes of the cells that contributes to the Na+ load on the pump and Na+ recycling participates in the regulation of the Na+ concentration of the Na+ transport pool of these epithelial cells.
开发了一种同位素方法来测量蛙皮跨上皮钠转运池的细胞内钠含量。分离的上皮组织（无真皮）用24Na进行不对称标记，从顶端（Aa）或基底外侧（Ab）溶液中标记，或对称标记（Aab）。在1 mM哇巴因、100 μM氨氯吡咪和1 mM速尿存在的情况下进行24Na洗脱动力学实验，以确定转运池中的钠，这些物质可将冷钠和24Na捕获在转运池中。在对照上皮组织中，Aab平均为64.1 neq/cm2（13.9 mM），用100 μM氨氯吡咪最大程度抑制顶端膜钠内流会使Aab降至24.3 neq/cm2（5.3 mM）。哇巴因使Aab在30分钟内显著增加至303 neq/cm2，而氨氯吡咪对顶端膜钠内流的抑制显著降低了哇巴因引起的Aab增加速率（对照中为7.3 neq·cm-2·min-1，氨氯吡咪存在时为1.7 neq·cm-2·min-1）。这些数据部分证实了在细胞基底外侧膜存在重要的钠通透性，这在对细胞基底外侧膜双向24Na通量的单独研究中得到了测量。两组数据均支持这样的观点，即细胞基底外侧膜存在显著的钠再循环，这有助于泵上的钠负荷，且钠再循环参与了这些上皮细胞钠转运池钠浓度的调节。
