[H-3] PTDINS HYDROLYSIS IN POSTMORTEM HUMAN BRAIN MEMBRANES IS MEDIATED BY THE G-PROTEINS G(Q 11) AND PHOSPHOLIPASE C-BETA/

A method utilizing exogenously added [H-3]PtdIns incubated with membra nes prepared from postmortem human brain has been shown to provide a m eans of measuring agonist-induced, guanosine 5'-O-(thiotriphosphate) ( GTP[SI)-dependent hydrolysis of [H-3]PtdIns, thus allowing investigati ons of the activity of the phosphoinositide second-messenger system in accessible human brain tissue. Agonists inducing [H-3]PtdIns hydrolys is include carbachol, trans-1-aminocyclopentyl-1,3-dicarboxylate (ACPD ; a glutamatergic metabotropic receptor agonist), serotonin and ATP, w ith the latter two agonists producing the largest responses. In additi on to ATP, [H-3]PtdIns hydrolysis was induced by ADP and by 2-methylth io-ATP, indicating that P-2-purinergic receptors mediate this process. Subtype-selective antibodies were used to identify G(q/11) and phosph olipase C-beta as the G-protein and phospholipase C subtypes that medi ated GTP[S]-induced and agonist-induced [H-3]PtdIns hydrolysis. These results demonstrate that this method reveals that agonist-induced, GTP [S]-dependent [H-3]PtdIns hydrolysis is retained in postmortem human b rain membranes with properties similar to rat brain. This method shoul d allow studies of the modulation of phosphoinositide hydrolysis in hu man brain and investigations of potential alterations in postmortem br ain from subjects with neurological and psychiatric diseases.