Voltage-dependent modulation of calcium current by GTP gamma S and dopamine in cultured frog pituitary melanotrophs.
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.
Valentijn
J A
JA
European Institute for Peptide Research, Laboratory of Molecular Endocrinology, CNRS URA 650, UA INSERM, University of Rouen, Mont-Saint-Aignan, France.
Louiset
E
E
Vaudry
H
H
Cazin
L
L
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*
D015220:Calcium Channels; D001464:Barium; D016244:Guanosine 5'-O-(3-Thiotriphosphate); D009074:Melanocyte-Stimulating Hormones; D004298:Dopamine