Hydrolysis of phosphatidylinositol 4,5-bisphosphate mediates calcium-induced inactivation of TRPV6 channels

TRPV6 is a member of the transient receptor potential superfamily of ion channels that facilitates Ca2+ absorption in the intestines. These channels display high selectivity for Ca2+, but in the absence of divalent cations they also conduct monovalent ions. TRPV6 channels have been shown to be inactivated by increased cytoplasmic Ca2+ concentrations. Here we studied the mechanism of this Ca2+ -induced inactivation. Monovalent currents through TRPV6 substantially decreased after a 40-s application of Ca butnotBa Wealsoshowthat Ca2+,but not Ba2+ ,influx via TRPV6 induces depletion of phos phatidylinositol 4,5-bisphosphate (PI(4,5)P-2 or PIN2) and the formation of inositol 1,4,5-trisphosphate. Dialysis of DiC(8) PI(4,5)P-2 through the patch pipette inhibited Ca2+ -dependent inactivation of TRPV6 currents in whole-cell patch clamp experiments. PI(4,5)P-2 also activated TRPV6 currents in excised patches. PI(4)P, the precursor of PI(4,5)P-2, neither activated TRPV6 in excised patches nor had any effect on Ca2+ -induced inactivation in whole-cell experiments. Conversion of PI(4,5)P-2 to PI(4)P by a rapamycin-inducible PI(4,5)P-2 5-phosphatase inhibited TRPV6 currents in whole-cell experiments. Inhibiting phosphatidylinositol 4 kinases with wortmannin decreased TRPV6 currents and Ca2+ entry into TRPV6-expressing cells. We propose that Ca2+ influx through TRPV6 activates phospholipase C and the resulting depletion of PI(4,5)P-2 contributes to the inactivation of TRPV6.