Regulation of single Cl- channel conductance by insulin and tyrosine phosphatase

The apical membrane of distal nephron epithelium (A6) had a Ca(2+)-activated outwardly rectifying Cl- channel with single-channel conductances of 3 pS for outward current and 0.8 pS for inward current. The single-channel conductance for inward current was dependent on cytosolic Ca2+ concentration. Insulin increased the single-channel conductance for the inward current by increasing Ca2+ sensitivity about 300-fold. The insulin action was diminished by vanadyl hydroperoxide (vanadate, an inhibitor of protein tyrosine phosphatase (PTP)). Application of protein tyrosine kinase, p60c-src, reversibly diminished the insulin-induced increase in single-channel conductance. Further, the application of PTP to the cytosolic surface of the inside-out patch membrane, like insulin, increased single-channel conductance. PTP-mediated dephosphorylation of the phospho-tyrosine of the channel protein, as a mechanism of intracellular signaling of insulin action, is a novel mechanism for regulating single-channel conductance by modulating Ca2+ sensitivity.