The interaction between β- and α 2-adrenoceptors in cerebral cortical membranes: Isoproterenol-induced increase in [ 3H]clonidine binding in rats

Abstract

The pretreatment of rat cerebral cortical membranes with 10 or 100 μM isoproterenol at 37°C for 40 min caused a significant elevation of the B max value of [ 3H]clonidine binding but pretreatment at 4°C did not affect the value. The isoproterenol-induced increase in the B max value of the binding was higher in 50 mM Tris-HCl buffer (pH 7.7) than in Krebs-Ringer solution. In 50 mM Tris-HCl buffer (pH 7.7), treatment with isoproterenol reduced the B max value of [ 3H]dihydroalprenolol binding but neither K d nor B max of [ 3H]WB 4101 binding was affected by this treatment. Fitty μM propranolol or 100 μM GTP produced a significant reduction in isoproterenol-induced elevation of the B max value of [ 3H]clonidine binding. In contrast, 100 μM cyclic AMP did not affect the control binding and 0.1 or 1 mM theophylline did not affect the isoproterenol-induced elevation of the binding. The only B max value in high affinity binding of [ 3H]clonidine was increased by isoproterenol. It is suggested that isoproterenol increases the density of α 2-adrenoceptors in a temperature-dependent manner. The direct interaction between β- and α 2-receptor molecules and/or their indirect interaction, mediated by GTP regulatory proteins, would exist in the cerebral cortical membranes of rats.