Nagami G T
Nephrology Section, Veterans Administration Medical Center, West Los Angeles, California 90073.
J Clin Invest. 1990 Jul;86(1):32-9. doi: 10.1172/JCI114702.
To determine the effects of acute changes in K+ concentration in vitro on ammonia production and secretion by the proximal tubule, we studied mouse S2 segments perfused with and bathed in Krebs-Ringer bicarbonate buffers containing various K+ concentrations. All bath solutions contained L-glutamine as the ammoniagenic substrate. High bath and luminal K+ concentrations (8 mM), but not high luminal K+ concentration alone, inhibited total ammonia production rates by 26%, while low bath and luminal K+ concentrations (2 mM), but not low luminal K+ concentration alone, stimulated total ammonia production rates by 33%. The stimulation of ammonia production by low bath K+ concentration was not observed when L-glutamine was added to the luminal perfusion solution. On the other hand, high luminal K+ concentration stimulated, while low luminal K+ concentration inhibited, net luminal secretion of total ammonia in a way that was: (a) independent of total ammonia production rates, (b) independent of Na(+)-H+ exchange activity, and (c) not due to changes in transepithelial fluxes of total ammonia. These results suggest that luminal potassium concentration has a direct effect on cell-to-lumen transport of ammonia.
为了确定体外钾离子浓度的急性变化对近端小管氨生成和分泌的影响，我们研究了用含有不同钾离子浓度的 Krebs-Ringer 碳酸氢盐缓冲液灌注并浸泡的小鼠 S2 节段。所有浴液均含有 L-谷氨酰胺作为产氨底物。高浴液和管腔钾离子浓度（8 mM），但单独的高管腔钾离子浓度则不会，使总氨生成速率降低 26%，而低浴液和管腔钾离子浓度（2 mM），但单独的低管腔钾离子浓度则不会，使总氨生成速率提高 33%。当将 L-谷氨酰胺添加到管腔灌注液中时，未观察到低浴液钾离子浓度对氨生成的刺激作用。另一方面，高管腔钾离子浓度刺激，而低管腔钾离子浓度抑制总氨的净管腔分泌，其方式为：（a）独立于总氨生成速率，（b）独立于钠氢交换活性，（c）不是由于总氨跨上皮通量的变化。这些结果表明管腔钾离子浓度对氨的细胞至管腔转运有直接影响。
