Dose-dependent down-regulation of beta-adrenoceptors by isoproterenol in rat C6 glioma cells.

Nano- and micromolar isoproterenol concentrations were compared by studying cyclic AMP, beta-adrenoceptor density and beta 1-adrenoceptor mRNA in rat C6 glioma cells. 1 microM isoproterenol significantly changed all parameters at 15-30 min. The beta 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 C6 cells following physiologically low agonist concentrations.