title: Irreversible inactivation of beta-adrenergic receptors of C6 glioma cells. Synthesis and study of a thiol derivative of propranolol.
abstract: The beta-adrenergic receptor of C6 glioma cells contains a disulfide bridge which can be reduced by dithiothreitol (DTT). On intact cells, N-ethylmaleimide (NEM) (5 mM) does not change the affinity of [3H] H2-alprenolol ([3H] DHA) but reduces the total number of beta-adrenergic cell receptors by 21 +/- 3 per cent ; (N = 3). After receptor reduction by DTT, NEM irreversibly blocks the accessibility of the beta-adrenergic receptors to [3H]DHA. On isolated membranes, incubation in the presence of either NEM (5 mM) or isoproterenol (5.10(-7) M) does not significantly modify the total number of beta-adrenergic receptors accessible to [3H]DHA. Incubation of membranes with both NEM and isoproterenol reduces the number of binding sites by 33 +/- 2 per cent ; (N = 3). A thiol derivative of propranolol was synthetized. Its affinity is 10 times lower than that of propranolol. This sulfur derivative reduces the total number of beta-adrenergic receptors by 22 +/- 3 per cent (N = 3) when incubated with the native receptor and by 55 +/- 4 per cent (N = 4) when incubated with the reduced receptor. DTT does not significantly reverse the blockade induced by propranolol-SH. A model is proposed for explaining these results.
mesh_terms: D000262:Adenylyl Cyclases / Q000378:metabolism; D000818:Animals; D002460:Cell Line; D004229:Dithiothreitol / Q000494:pharmacology; D005033:Ethylmaleimide / Q000494:pharmacology; D005910:Glioma / Q000378:metabolism*; D007545:Isoproterenol / Q000494:pharmacology; D007700:Kinetics; D009374:Neoplasms, Experimental / Q000378:metabolism; D011433:Propranolol / Q000031:analogs & derivatives* / Q000138:chemical synthesis / Q000378:metabolism; D051381:Rats; D011941:Receptors, Adrenergic / Q000378:metabolism*; D011943:Receptors, Adrenergic, beta / Q000187:drug effects / Q000378:metabolism*
chemical_list: D011941:Receptors, Adrenergic; D011943:Receptors, Adrenergic, beta; C026477:N-(S-methyl)mercaptoethylpropranolol; C026476:N-mercaptoethylpropranolol; D011433:Propranolol; D000262:Adenylyl Cyclases; D007545:Isoproterenol; D005033:Ethylmaleimide; D004229:Dithiothreitol