title: Inhibition of inwardly rectifying K+ current by external Ca2+ ions in freshly isolated rabbit osteoclasts.
abstract: 1. Regulation of membrane potential by extracellular Ca2+ concentration ([Ca2+]o) was examined in freshly isolated rabbit osteoclasts. 2. The resting membrane potential of osteoclasts was close to the K+ equilibrium potential in 1 mM Ca2+ medium. An elevation of [Ca2+]o caused membrane depolarization, accompanied by a decrease in the membrane conductance. 3. The inwardly rectifying K+ current observed under voltage clamp was dose-dependently inhibited by an elevation of [Ca2+]o, which explained the membrane depolarization caused by high [Ca2+]o. 4. Other divalent cations also inhibited the inwardly rectifying K+ current with the following order of potency: Ca2+ < Ni2+ < or = Co2+ < Cd2+. 5. In the presence of intracellular GTP gamma S the inwardly rectifying K+ current was irreversibly inhibited by [Ca2+]o, whereas the inhibition of the inwardly rectifying K+ current was greatly attenuated by intracellular application of GDP beta S. 6. Pertussis toxin (PTX) treatment did not abolish the inhibition of the inwardly rectifying K+ current caused by [Ca2+]o. 7. These results suggest that inwardly rectifying K+ channels in osteoclasts were regulated by a PTX-insensitive G-protein, which was coupled to the putative Ca2+ receptor or sensor on the cell membrane.
authors.affiliation: Fourth Department of Internal Medicine, University of Tokyo School of Medicine, Japan.
authors.forename: N
authors.initials: N
authors.lastname: Yamashita
authors.forename: T
authors.initials: T
authors.lastname: Ishii
authors.forename: E
authors.initials: E
authors.lastname: Ogata
authors.forename: T
authors.initials: T
authors.lastname: Matsumoto
mesh_terms: D000818:Animals; D002118:Calcium / Q000494:pharmacology*; D002413:Cations, Divalent / Q000494:pharmacology; D019204:GTP-Binding Proteins / Q000378:metabolism; D016244:Guanosine 5'-O-(3-Thiotriphosphate) / Q000494:pharmacology; D006153:Guanosine Diphosphate / Q000031:analogs & derivatives / Q000494:pharmacology; D066298:In Vitro Techniques; D017136:Ion Transport / Q000187:drug effects; D008564:Membrane Potentials / Q000187:drug effects; D010010:Osteoclasts / Q000187:drug effects* / Q000378:metabolism*; D037342:Pertussis Toxin; D011188:Potassium / Q000378:metabolism*; D015221:Potassium Channels / Q000187:drug effects / Q000378:metabolism; D011817:Rabbits; D013873:Thionucleotides / Q000494:pharmacology; D010566:Virulence Factors, Bordetella / Q000494:pharmacology
chemical_list: D002413:Cations, Divalent; D015221:Potassium Channels; D013873:Thionucleotides; D010566:Virulence Factors, Bordetella; D006153:Guanosine Diphosphate; D016244:Guanosine 5'-O-(3-Thiotriphosphate); C023427:guanosine 5'-O-(2-thiodiphosphate); D037342:Pertussis Toxin; D019204:GTP-Binding Proteins; D011188:Potassium; D002118:Calcium