title: Receptor-induced depletion of phosphatidylinositol 4,5-bisphosphate inhibits inwardly rectifying K+ channels in a receptor-specific manner.
abstract: Phosphatidylionsitol 4,5-bisphosphate (PIP(2)), a substrate of phospholipase C, has recently been recognized to regulate membrane-associated proteins and act as a signal molecule in phospholipase C-linked Gq-coupled receptor (GqPCR) pathways. However, it is not known whether PIP(2) depletion induced by GqPCRs can act as receptor-specific signals in native cells. We investigated this issue in cardiomyocytes where PIP(2)-dependent ion channels, G protein-gated inwardly rectifying K(+) (GIRK) and inwardly rectifying background K(+) (IRK) channels, and various GqPCRs are present. The GIRK current was recorded by using the patch-clamp technique during the application of 10 microM acetylcholine. The extent of receptor-mediated inhibition was estimated as the current decrease over 4 min while taking the GIRK current (I(GIRK)) value during a previous stimulation as the control. Each GqPCR agonist inhibited I(GIRK) with different potencies and kinetics. The extents of inhibition induced by phenylephrine, angiotensin II, endothelin-1, prostaglandin F2alpha, and bradykinin at supramaximal concentrations were (mean +/- SE) 32.1 +/- 0.6%, 21.9 +/- 1.4%, 86.4 +/- 1.6%, 63.7 +/- 4.9%, and 5.7 +/- 1.9%, respectively. GqPCR-induced inhibitions of I(GIRK) were not affected by protein kinase C inhibitor (calphostin C) but potentiated and became irreversible when the replenishment of PIP(2) was blocked by wortmannin (phosphatidylinositol kinase inhibitor). Loading the cells with PIP(2) significantly reduced endothelin-1 and prostaglandin F2alpha-induced inhibition of I(GIRK). On the contrary, GqPCR-mediated inhibitions of inwardly rectifying background K(+) currents were observed only when GqPCR agonists were applied with wortmannin, and the effects were not parallel with those on I(GIRK). These results indicate that GqPCR-induced inhibition of ion channels by means of PIP(2) depletion occurs in a receptor-specific manner.
authors.affiliation: National Research Laboratory for Cell Physiology, Department of Physiology, Seoul National University College of Medicine, 28 Yonkeun-Dong, Chongno-Ku, Seoul 110-799, Korea.
authors.forename: Hana
authors.initials: H
authors.lastname: Cho
authors.forename: Doyun
authors.initials: D
authors.lastname: Lee
authors.forename: Suk Ho
authors.initials: SH
authors.lastname: Lee
authors.forename: Won-Kyung
authors.initials: WK
authors.lastname: Ho
mesh_terms: D000109:Acetylcholine / Q000494:pharmacology; D000730:Androstadienes / Q000494:pharmacology; D000804:Angiotensin II / Q000494:pharmacology; D000818:Animals; D001920:Bradykinin / Q000494:pharmacology; D015237:Dinoprost / Q000494:pharmacology; D019332:Endothelin-1 / Q000494:pharmacology; D051676:G Protein-Coupled Inwardly-Rectifying Potassium Channels; D043802:GTP-Binding Protein alpha Subunits, Gq-G11 / Q000187:drug effects / Q000378:metabolism*; D066298:In Vitro Techniques; D051379:Mice; D032383:Myocytes, Cardiac / Q000187:drug effects / Q000378:metabolism; D009281:Naphthalenes / Q000494:pharmacology; D018408:Patch-Clamp Techniques; D010656:Phenylephrine / Q000494:pharmacology; D019269:Phosphatidylinositol 4,5-Diphosphate / Q000378:metabolism*; D024661:Potassium Channels, Inwardly Rectifying / Q000037:antagonists & inhibitors* / Q000187:drug effects / Q000378:metabolism; D000077191:Wortmannin
chemical_list: D000730:Androstadienes; D019332:Endothelin-1; D051676:G Protein-Coupled Inwardly-Rectifying Potassium Channels; D009281:Naphthalenes; D019269:Phosphatidylinositol 4,5-Diphosphate; D024661:Potassium Channels, Inwardly Rectifying; D000804:Angiotensin II; D010656:Phenylephrine; D015237:Dinoprost; D043802:GTP-Binding Protein alpha Subunits, Gq-G11; C058819:calphostin C; D000109:Acetylcholine; D001920:Bradykinin; D000077191:Wortmannin