Facilitation of Ca2+ action potential frequency by a small G protein Rab3A in rat pituitary GH3 cells.
GH3 pituitary cells have high tendency to exhibit spontaneous Ca2+ action potentials and their frequency (Ca2+ APF) is increased by treatment with thyrotropin-releasing hormone (TRH). Although spontaneous Ca2+ firing was thought to be significant for the induction of oscillations in cytosolic Ca2+ concentration ([Ca2+]i), little attempt to elucidate the mechanism has been done so far. We demonstrate here that spontaneous Ca2+ APF in GH3 cells was increased 1.5-3 fold, comparable to that for TRH, by injection of guanosine 5'-0-3-thiotriphosphate (GTPgammaS), rab3A effector domain peptide, and phorbol-dibutyrate (PDBu), whereas guanosine 5'-O-(2-thiodiphosphate) (GDPbetaS), H-rab5 peptide, ras peptide, and 4 alpha-phorbol did not. The enhancement of Ca2+ firing by rab3A effector domain peptide was blocked by a protein kinase C (PKC) inhibitor, PKC(19-36). The present study suggests that the spontaneous Ca2+APF may be controlled by small G protein phosphorylated by PKC.
Suzuki
N
N
Department of Physiology, School of Medicine, Kitasato University, Sagamihara, Japan. suzuchan@med.kitasato-u.ac.jp
Hirono
M
M
Takagi
H
H
Yoshioka
T
T
D000200:Action Potentials; D000818:Animals; D002118:Calcium / Q000378:metabolism*; D004791:Enzyme Inhibitors / Q000494:pharmacology; D019204:GTP-Binding Proteins / Q000037:antagonists & inhibitors / Q000378:metabolism*; D016244:Guanosine 5'-O-(3-Thiotriphosphate) / Q000494:pharmacology; D006153:Guanosine Diphosphate / Q000031:analogs & derivatives / Q000494:pharmacology; D018408:Patch-Clamp Techniques; D010446:Peptide Fragments / Q000494:pharmacology; D010455:Peptides / Q000494:pharmacology; D015240:Phorbol 12,13-Dibutyrate / Q000494:pharmacology; D010704:Phorbols / Q000494:pharmacology; D010902:Pituitary Gland / Q000166:cytology / Q000378:metabolism*; D011493:Protein Kinase C / Q000037:antagonists & inhibitors / Q000378:metabolism / Q000494:pharmacology; D051381:Rats; D013873:Thionucleotides / Q000494:pharmacology; D013973:Thyrotropin-Releasing Hormone / Q000494:pharmacology; D014407:Tumor Cells, Cultured; D020692:rab3 GTP-Binding Proteins; D020696:rab5 GTP-Binding Proteins; D018631:ras Proteins / Q000378:metabolism
D004791:Enzyme Inhibitors; D010446:Peptide Fragments; D010455:Peptides; D010704:Phorbols; D013873:Thionucleotides; C072093:protein kinase C (19-36); C083869:rab3AL peptide; D006153:Guanosine Diphosphate; D015240:Phorbol 12,13-Dibutyrate; D016244:Guanosine 5'-O-(3-Thiotriphosphate); D013973:Thyrotropin-Releasing Hormone; C023427:guanosine 5'-O-(2-thiodiphosphate); D011493:Protein Kinase C; D019204:GTP-Binding Proteins; D020692:rab3 GTP-Binding Proteins; D020696:rab5 GTP-Binding Proteins; D018631:ras Proteins; D002118:Calcium; C033085:phorbol