Specific Binding of [3H]Lysine-Vasopressin to Pig Kidney Plasma Membranes RELATIONSHIP OF RECEPTOR OCCUPANCY TO ADENYLATE CYCLASE ACTIVATION

摘要: Abstract A plasma membrane fraction was prepared from pig kidney medulla. It contained lysine-vasopressin-sensitive adenylate cyclase activity (maximum activation: 4- to 6-fold, apparent Km value for the hormone: about 5 x 10-9 m). Lysine-vasopressin not inactivated by preparation even at low hormonal concentrations. The specific [3H]lysine-vasopressin (vasopressin) binding sites found are probably involved in activation; occurred a concentration range giving dose-dependent activation of cyclase. Relative affinities vasopressin, oxytocin, (O-methyl)-tyrosine2-oxytocin and angiotensin (vasopressin g oxytocin (O-Me)-Tyr2-oxy angiotensin) were similar. Nonspecific binding, i.e. which could be inhibited 10-5 m unlabeled represented 12.5% 10-8 [3H]vasopressin. For all concentrations, [3H]vasopressin increased with time up an equilibrium value. reversible. course hormone-receptor complex formation highly temperature- hormone concentration-dependent. Dissociation association rate constants 30° varied 0.02 0.088 min-1 k-1, 1.3 10+7 3.0 m-1 k1. same enzyme preparation, k-1:k1 ratio very close deduced half maximum equilibrium. When measured as function after addition hormone, progressive. required reach is similar that needed concentration. These data suggest receptor occupancy. Reversal also different values occupancy, it increment drops total occupancy increases.