alpha sub(2A)-Adrenoceptor-specific Stimulation of [ super(35)S]GTP gamma S Binding to Membrane Preparations of Rat Frontal Cortex

Functional activation of alpha sub(2A) adrenergic receptors in the crude membranes from rat frontal cortex was studied by a [ super(35)S]-guanosine 5'-O-( gamma -thiotriphosphate) ([ super(35)S]GTP gamma S) binding assay. alpha sub(2A) agonists UK14304 and guanfacine decreased the ability of GDP to compete with [ super(35)S]GTP gamma S binding to the membranes and 0.1 mM GDP was found to be optimal for the following functional experiments. However, even after careful optimization of experimental conditions the specificity of ligands for rat alpha sub(2) adrenoceptors were not sufficient, as agonists as well as antagonists became activators of other signal transduction systems before achieving their maximal effect in the alpha sub(2A)-adrenergic system. Only using compromising concentration of agonist (up to 1 mu M UK14304) and antagonist (up to 1 mu M RS79948) to inhibit agonist's effect, allowed us to filtrate out alpha sub(2A) specific effect for characterization of signal transduction in rat frontal cortex membranes for the comparison efficacies of this system for different animals from behavioral experiments.