Characterization of imido [8-(3)H] guanosine 5'-triphosphate binding sites to rat brain membranes.

Besides their well-defined intracellular roles in transmembrane signals transduction, guanine derivatives play important roles by acting from the outside of neural cell membranes. These roles are mediated by two different pool sites in cell membranes: G proteins, which bind to specific (GDP and GTP) intracellular guanine derivatives, and sites that bind to extracellular guanine derivatives. In this study we investigated some methodological characteristics of both guanine derivatives binding sites (intracellular and extracellular) in rat brain neural membranes. By investigating the binding of a poorly hydrolyzed GTP analogue and the adenylate cyclase activity in neural membranes, we observed some distinctiveness of guanine derivatives binding sites: stability to washing procedures (extracellular) and modulation of adenylate cyclase activity (intracellular). These results allow dealing with each site separately, which could be useful for discriminating the roles of extracellular and intracellular guanine derivatives in the central nervous system.