| Abstract: | Effects of pre-treatment of synaptic membranes with beta-adrenoceptor agonists and cholera toxin on 3H]clonidine and 3H]yohimbine binding were examined in rat cerebral cortex. Pre-incubation of cerebral cortical membranes with isoproterenol (10 or 200 microM) or dobutamine (1, 10 or 200 microM) at 37 degrees C for 40 min caused a significant elevation of specific 3H]clonidine binding but treatment with salbutamol (10 or 200 microM) did not. Scatchard analysis showed that 200 microM isoproterenol treatment resulted in a significant elevation of high affinity component of 3H]clonidine binding which was significantly decreased by the addition of 10 microM GTP. A significant elevation in high affinity 3H]clonidine binding was observed by treatment with 100 micrograms/ml cholera toxin, while a significant decrease in low affinity one was by the treatment. Specific 3H]yohimbine binding was also elevated by 10 or 200 microM isoproterenol treatment. It is suggested that stimulation of beta-receptors, presumably beta 1-subtype, could elevate the number of agonist and antagonist binding sites in alpha 2-receptors in synaptic membranes by partially mediated by stimulatory and/or inhibitory GTP binding regulatory proteins. |
