Metabolism of adrenergic receptors and adenylate cyclase

The alpha 1 and beta-adrenergic receptor metabolism was studied at cell confluency in BC3H1 and C6 glioma cells. After their irreversible blockade with phenoxybenzamine and a bromoacetyl derivative of pindolol (Br-AAM-pindolol) respectively the receptor reappearance allows to determine a half life of 23 hours for the alpha 1-adrenergic receptor in BC3H1 and a quasi absence of beta-adrenergic receptor metabolism in C6 glioma cells at confluency. In contrast, beta-adrenergic receptor is rapidly synthesized during cell division. This metabolic stability of beta-adrenergic receptor at confluency was also observed in BC3H1 cells using the heavy isotope labeling of the beta-adrenergic receptor (half life of 8 days). This stability was also confirmed by the observation that at confluency in C6 glioma cells, beta adrenergic receptors reappeared at the cell surface after a complete down-regulation. In parallel with the study of the half life of adrenergic receptors, we determined in BC3H1 the half life of the forskolin stimulated catalytic unit of the adenylate cyclase using heavy isotope labeling method. In heavy amino-acid medium the apparent sedimentation coefficients of the adenylate cyclase increased from 7.4 +/- 0.04S (n = 36) to 8.4 +/- 0.03S (n = 13). This increase was due to the synthesis of new heavy molecule since it was blocked by cycloheximide. The analysis of the kinetic of synthesis of heavy molecules allowed to calculate a half life of 36 hours. The comparison between the half life of several regulatory membrane proteins in BC3H1 indicate that each of them has a specific metabolism.