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

Abstract

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 Ca2+, but not Ba2+. We also show that Ca2+, but not Ba2+, influx via TRPV6 induces depletion of phosphatidylinositol 4,5-bisphosphate (PI(4,5)P2 or PIP2) and the formation of inositol 1,4,5-trisphosphate. Dialysis of DiC8 PI(4,5)P2 through the patch pipette inhibited Ca2+- dependent inactivation of TRPV6 currents in whole-cell patch clamp experiments. PI(4,5)P2 also activated TRPV6 currents in excised patches. PI(4)P, the precursor of PI(4,5)P2, neither activated TRPV6 in excised patches nor had any effect on Ca2+-induced inactivation in whole-cell experiments. Conversion of PI(4,5)P2 to PI(4)P by a rapamycin-inducible PI(4,5)P2 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)P2 contributes to the inactivation of TRPV6. © 2008 by The American Society for Biochemistry and Molecular Biology, Inc.