The collecting duct is involved in the whole antinatriuretic effect of insulin, as indicated in vitro by the stimulatory effect of the hormone on ouabain-sensitive 86Rb+ uptake. Since Na+,K(+)-ATPase drives Na+ reabsorption, the contribution of the Na+ pump to the effect of insulin was investigated in rat isolated cortical and outer medullary collecting duct. 2. Insulin enhanced ouabain-sensitive 86Rb+ uptake in the absence, as well as in the presence, of either 5 x 10(-4) M amiloride or 10(-3) M hydrochlorothiazide (HCT). Maximal ouabain-sensitive 86Rb+ uptake, measured in Na(+)-loaded tubules, was also enhanced by insulin. The insulin effect persisted both in the absence of external Na+, when the Na+,K(+)-ATPase operates in a Rb(+)-Rb+ exchange mode, and in tubules depolarized by a high external concentration (20 mM) of Rb+ or by addition of 3 mM Ba2+. 3. Insulin treatment did not alter the intracellular Na and K concentrations, the specific binding of [3H]ouabain measured in intact tubules, or the hydrolytic activity of Na+,K(+)-ATPase measured after permeabilization of the tubule cells. 4. In conclusion, in the rat collecting duct, insulin increased Na+,K(+)-ATPase-mediated cation transport independently of Na+ availability, membrane potential and recruitment of pump units. The effect of insulin was lost after cell permeabilization, suggesting the presence of a cytosolic factor which controls the turnover of Na+,K(+)-ATPase.
摘要
集合管参与胰岛素的整个抗利尿钠作用，如在体外实验中，该激素对哇巴因敏感的86Rb+摄取具有刺激作用所表明的那样。由于Na+,K(+)-ATP酶驱动Na+重吸收，因此在大鼠离体皮质和外髓集合管中研究了Na+泵对胰岛素作用的贡献。2. 在不存在或存在5×10(-4) M氨氯吡咪或10(-3) M氢氯噻嗪（HCT）的情况下，胰岛素均可增强哇巴因敏感的86Rb+摄取。在装载Na+的肾小管中测得的最大哇巴因敏感的86Rb+摄取也被胰岛素增强。当Na+,K(+)-ATP酶以Rb(+)-Rb+交换模式运行时，在没有外部Na+的情况下，以及在被高外部浓度（20 mM）的Rb+或添加3 mM Ba2+去极化的肾小管中，胰岛素的作用均持续存在。3. 胰岛素处理并未改变细胞内Na和K的浓度、完整肾小管中测得的[3H]哇巴因的特异性结合，或肾小管细胞通透后测得的Na+,K(+)-ATP酶的水解活性。4. 总之，在大鼠集合管中，胰岛素增加了Na+,K(+)-ATP酶介导的阳离子转运，而与Na+的可用性、膜电位和泵单位的募集无关。细胞通透后胰岛素的作用消失，这表明存在一种控制Na+,K(+)-ATP酶周转的胞质因子。
