Insulin enhances the stimulatory action of genistein on Cl- transport by modifying translocation of Cl- channel and Na+/K+/2Cl- cotransporter in renal epithelial A6 cells

Abstract

We reported that genistein stimulates Cl- transport by activating apical Cl- channels and basolateral Na+/K+/2Cl- cotransporter (NKCC) in renal epithelial A6 cells. In this study, we found that insulin enhanced the genistein action on Cl- transport. Therefore, we determined whether insulin shows the enhancement by affecting translocation of Cl- channel and/or NKCC in genistein-treated cells. Brefeldin A (BFA) diminished the Cl- transport by decreasing the NPPB-sensitive conductance (Gt) and the action was less effective in insulin-treated cells. On the other hand, pretreatment with MG132 caused further increases in the Cl- transport without affecting the NPPB-sensitive Gt in both insulin-treated and -untreated cells, however MG132 was much more effective in insulin-treated cells than in insulin-untreated cells. These results suggest that: 1) the enhancement of genistein action by insulin occurs through translocation of the Cl- channel to the apical membrane, 2) insulin shows the enhancement by increasing both rates of insertion and endocytosis of NKCC, 3) the insulin action is larger in the insertion of NKCC than the endocytosis. Supported by JSPS 15659052 (YM), 15590189 (NN), 15790120 (HM). [Jpn J Physiol 54 Suppl:S69 (2004)]