title: Voltage-dependent modulation of calcium current by GTP gamma S and dopamine in cultured frog pituitary melanotrophs.
abstract: Dopamine (1 microM) reversibly scaled down barium current through high-voltage activated (HVA) calcium channels but had little effect on the time course of current activation in cultured frog melanotrophs. Intracellular perfusion with guanosine-5'-O-(3-thiotriphosphate) (GTP gamma S; 100 microM) sustained the effect of dopamine. Moreover, GTP gamma S drastically slowed down the current activation kinetics. The latter effect was in part reversed by dopamine. A conditioning prepulse to +70 mV facilitated the current in GTP gamma S-dialyzed cells but not in cells exposed to dopamine. These results suggest the existence of a dual G protein-mediated mechanism for reducing HVA calcium current.
authors.affiliation: European Institute for Peptide Research, Laboratory of Molecular Endocrinology, CNRS URA 650, UA INSERM, University of Rouen, Mont-Saint-Aignan, France.
authors.forename: J A
authors.initials: JA
authors.lastname: Valentijn
authors.forename: E
authors.initials: E
authors.lastname: Louiset
authors.forename: H
authors.initials: H
authors.lastname: Vaudry
authors.forename: L
authors.initials: L
authors.lastname: Cazin
mesh_terms: D000818:Animals; D001001:Anura; D001464:Barium / Q000502:physiology; D015220:Calcium Channels / Q000187:drug effects / Q000502:physiology*; D002478:Cells, Cultured; D004298:Dopamine / Q000494:pharmacology*; D004553:Electric Conductivity; D016244:Guanosine 5'-O-(3-Thiotriphosphate) / Q000494:pharmacology*; D009074:Melanocyte-Stimulating Hormones / Q000378:metabolism*; D010902:Pituitary Gland / Q000166:cytology / Q000502:physiology*
chemical_list: D015220:Calcium Channels; D001464:Barium; D016244:Guanosine 5'-O-(3-Thiotriphosphate); D009074:Melanocyte-Stimulating Hormones; D004298:Dopamine