Synergic action of insulin and genistein on Na+/K+/2Cl‐ cotransporter (NKCC) in renal epithelium

Abstract

We studied the effect of insulin and quercetin on Cl- secretion in renal epithelial A6 cells by estimating Cl- channel activity and Cl− secretion by measuring NPPB-sensitive transepithelial conductance (Gt) and short-circuit current (Isc). Pretreatment with 1mM insulin for 24h had no effects on Gt or Isc, but increased the Isc with no effects on Gt in A6 cells treated with MG132 (100mM for 2h) that inhibits endocytosis of proteins at the plasma membrane into the cytosolic space. Genistein (100mM) induced sustained increases in Gt and Isc, which were diminished by brefeldin A. Co-application of insulin and genistein synergically stimulated the Isc without any effects on Gt. These observations suggest that: 1) insertion and endocytosis of NKCC are stimulated by insulin, 2) the insulin-induced stimulation of NKCC insertion into the basolateral membrane is offset by the stimulatory action on NKCC endocytosis from the basolateral membrane, 3) genistein stimulates both insertion of CFTR Cl− channel into the apical membrane and insertion of NKCC into the basolateral membrane, and 4) insulin and genistein synergically stimulated NKCC insertion into the basolateral membrane. Supported by JSPS (17390057, 17590191).