ALTERATION OF TUBULIN-G(I) PROTEIN-INTERACTION IN RAT CEREBRAL-CORTEXWITH AGING

The ability of the tubulin dimer to interact with and to modulate the G(i) function inhibiting adenylyl cyclase was examined in cerebral cor tex membranes from 2-month-old and 24-month-old rats. The hydrolysis-r esistant GTP analogue 5'-guanylylimidodiphosphate (GppNHp)-dependent i nhibition of adenylyl cyclase was significantly decreased in cerebral cortex membranes from 24-month-old rats. Tubulin, prepared from rat br ains by polymerization with GppNHp, caused inhibition of adenylyl cycl ase (similar to 28%) in 2-month-old rats. Tubulin-GppNHp-dependent inh ibition of adenylyl cyclase in 24-month-old rats was significantly att enuated (similar to 15%). In 2-month-old rats, when tubulin, polymeriz ed with the hydrolysis-resistant photoaffinity GTP analogue [P-32]P-3( 4- azidoanilido)-P-1-5'-GTP ([P-32]AAGTP), was incubated with cerebral cortex membranes, AAGTP was transferred from tubulin to G(i alpha). T ransfer of AAGTP from tubulin to G(i alpha) was reduced in 24-month-ol d rats. Furthermore, photoaffinity labeling of [P-32]AAGTP to G(i alph a) in cortex membranes was significantly decreased in 24-month-old rat s. No differences were observed in the amounts of G(s alpha), G(i alph a), or G(beta) subunits and tubulin, estimated by immunoblotting, in c ortex membranes from 2-month-old and 24-month-old rats. These results suggest that the ability of tubulin to interact with G(i) and thereby modulate the inhibitory regulation of adenylyl cyclase is reduced in t he cerebral cortex of 24-month-old rats.