Dose-dependent down-regulation of beta -adrenoceptors by isoproterenol in rat C sub(6) glioma cells

Nano- and micromolar isoproterenol concentrations were compared by studying cyclic AMP, beta -adrenoceptor density and beta sub(1)-adrenoceptor mRNA in rat C sub(6) glioma cells. 1 mu M isoproterenol significantly changed all parameters at 15-30 min. The beta sub(1)-antagonist metoprolol attenuated the response. No effects of nanomolar isoproterenol on these early changes were observed, although the density of beta -adrenoceptors was significantly reduced beginning at 12 h. The results indicate a different process for beta -adrenoceptor desensitization in C sub(6) cells following physiologically low agonist concentrations.