Transfected Go1 alpha inhibits the calcium dependence of beta-adrenergic stimulated cAMP accumulation in C6 glioma cells.

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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.