Transfected Go1 alpha inhibits the calcium dependence of beta-adrenergic stimulated cAMP accumulation in C6 glioma cells.
Increasing evidence indicates that heterotrimeric G proteins, and in particular Go, regulate ionic channel activities. In order to investigate the role of Go proteins in the modulation of the Ca2+ influx, C6 glioma cells were stably transfected with alpha o1 cDNA. Expression of the Go1 alpha protein was checked by Bordetella pertussis toxin-catalyzed ADP-ribosylation and Western blots using one- and two-dimensional gel analyses. Three clones were selected based on their degree of Go1 alpha expression. In alpha o1-transfected cells, cAMP accumulations, in response to isoproterenol or forskolin, were lower than in control cells. This inhibitory effect was a function of the amount of expressed Go1 alpha. In contrast, Go1 alpha expression was not followed by a significant inhibition of isoproterenol- or forskolin-stimulated adenylyl cyclase activities in particulate fractions. In C6 parental cells, 50-60% of the isoproterenol-induced cAMP accumulation was dependent on external Ca2+ concentration. This Ca(2+)-dependent cAMP accumulation was related to an induced transient Ca2+ influx. In transfected cells, expression of Go1 alpha inhibited the Ca2+ influx and the Ca(2+)-dependent component of isoproterenol-induced cAMP accumulation. In conclusion, beta-adrenergic agonists stimulate an entry of Ca2+ which exerts a positive feedback on cAMP production, and Go1 alpha blocks this positive feedback by inhibiting the Ca2+ influx.
Charpentier
N
N
Centre National de la Recherche Scientifique-Institut National de la Santé et de la Recherche Médicale de Pharmacologie-Endocrinologie, Montpellier, France.
Prézeau
L
L
Carrette
J
J
Bertorelli
R
R
Le Cam
G
G
Manzoni
O
O
Bockaert
J
J
Homburger
V
V
D000262:Adenylyl Cyclases / Q000378:metabolism; D000318:Adrenergic beta-Agonists / Q000494:pharmacology*; D000818:Animals; D015139:Blotting, Southern; D002118:Calcium / Q000378:metabolism*; D002463:Cell Membrane Permeability; D005576:Colforsin / Q000494:pharmacology; D000242:Cyclic AMP / Q000378:metabolism*; D015180:Electrophoresis, Gel, Two-Dimensional; D019204:GTP-Binding Proteins / Q000235:genetics / Q000378:metabolism*; D007545:Isoproterenol / Q000494:pharmacology; D007700:Kinetics; D009457:Neuroglia / Q000166:cytology / Q000378:metabolism; D051381:Rats; D014162:Transfection; D014407:Tumor Cells, Cultured
D000318:Adrenergic beta-Agonists; D005576:Colforsin; D000242:Cyclic AMP; D019204:GTP-Binding Proteins; D000262:Adenylyl Cyclases; D007545:Isoproterenol; D002118:Calcium