title: 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 Ca(2+) absorption in the intestines. These channels display high selectivity for Ca(2+), but in the absence of divalent cations they also conduct monovalent ions. TRPV6 channels have been shown to be inactivated by increased cytoplasmic Ca(2+) concentrations. Here we studied the mechanism of this Ca(2+)-induced inactivation. Monovalent currents through TRPV6 substantially decreased after a 40-s application of Ca(2+), but not Ba(2+). We also show that Ca(2+), but not Ba(2+), influx via TRPV6 induces depletion of phosphatidylinositol 4,5-bisphosphate (PI(4,5)P(2) or PIP(2)) and the formation of inositol 1,4,5-trisphosphate. Dialysis of DiC(8) PI(4,5)P(2) through the patch pipette inhibited Ca(2+)-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 Ca(2+)-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 Ca(2+) entry into TRPV6-expressing cells. We propose that Ca(2+) influx through TRPV6 activates phospholipase C and the resulting depletion of PI(4,5)P(2) contributes to the inactivation of TRPV6.
authors.affiliation: Department of Pharmacology and Physiology, University of Medicine and Dentistry of New Jersey-New Jersey Medical School, 185 South Orange Avenue, Newark, NJ 07103, USA.
authors.forename: Baskaran
authors.initials: B
authors.lastname: Thyagarajan
authors.forename: Viktor
authors.initials: V
authors.lastname: Lukacs
authors.forename: Tibor
authors.initials: T
authors.lastname: Rohacs
mesh_terms: D001464:Barium / Q000378:metabolism; D002118:Calcium / Q000378:metabolism; D015220:Calcium Channels / Q000378:metabolism*; D002460:Cell Line; D006801:Humans; D006868:Hydrolysis; D015544:Inositol 1,4,5-Trisphosphate / Q000378:metabolism; D007408:Intestinal Absorption / Q000502:physiology; D007413:Intestinal Mucosa / Q000378:metabolism; D017136:Ion Transport / Q000502:physiology; D018408:Patch-Clamp Techniques; D019269:Phosphatidylinositol 4,5-Diphosphate / Q000378:metabolism*; D013379:Substrate Specificity / Q000502:physiology; D050916:TRPV Cation Channels / Q000378:metabolism*; D010738:Type C Phospholipases / Q000378:metabolism
chemical_list: D015220:Calcium Channels; D019269:Phosphatidylinositol 4,5-Diphosphate; D050916:TRPV Cation Channels; C422827:TRPV6 protein, human; D001464:Barium; D015544:Inositol 1,4,5-Trisphosphate; D010738:Type C Phospholipases; D002118:Calcium