CHARACTERISTICS OF THE KINETICS OF INTERA CTION BETWEEN BETA-ADRENOCEPTORS OF RAT ERYTHROCYTES AND A SPECIFIC BLOCKER PROPRANOLOL

The main parameters of binding and competitive displacement of [H-3]pr opranolol were obtained for beta-adrenoceptors of white rat erythrocyt es. It has been shown that two molecules of [H-3]propranolol get linke d to one beta-adrenoceptor; two discrete pools of adrenoceptors differ ing in the affinity to the ligand and in their number on the erythrocy te membrane have been revealed. In binding experiments the dissociatio n constants (K(d)) of high-affinity and low-affinity pools differ by a factor of 17 and are, respectively, 0.92 +/- 0.22 nM and 15.39 +/- 2. 69 nM. The number of receptors on the cell differs by a factor of 9 (2 8 +/- 6 and 258 +/- 58). The maximal number of adrenoceptors per eryth rocytes is 286 +/- 57. In competitive displacement of [H-3]propranolol (8,19 nM) by propranolol, the values K (EC50) for the two pools of bi nding sites differ by a factor of 6 and are 0.47 +/- 0.07 muM and 2.94 +/- 0.32 muM. The number of the binding sites of the ligand is roughl y equal in the two pools and is 40 +/- 6 and 55 +/- 10 per cell. The s um number of binding sites is 96 +/- 8 units per cell. The value of th e inhibitor constant is 14.03 +/- 2.39 nM. The main parameters of the ligand-receptor interaction produced by the two methods gave the same quantitative characteristics of functional activity of beta-adrenocept ors of erythrocytes.