[A new mechanism of inhibiting adenylate cyclase involving a beta-adrenergic receptor].

The previously unknown mechanism of adenylate cyclase activity inhibition by catecholamines has been found. It is realized through a beta-adrenoreceptor in the smooth muscle of fresh-water mollusc Anodonta cygnea. As to its ligand-binding characteristics (one class of binding sites with Kd = 0.35 + 0.06 nM, a competitive series of ligands substitution: isoproterenol greater than adrenalin greater than propranolol greater than noradrenaline greater than serotonin = dopamine greater than phentolamine) as well as to negative regulation of the GTP affinity this receptor is similar to beta-adrenoreceptors of higher vertebrates. The dose-dependent inhibiting effect (to 50-60%) of isoproterenol and noradrenaline on the basal, GTP- and serotonin-stimulated activity of adenylate cyclase and cAMP level which is removed only by beta-adrenergic blockers is shown in vitro and in vivo. It is concluded that inhibition of adenylate cyclase activity by catecholamines in the muscular tissue of the mollusc is realized via beta-adrenoreceptor.