Effects of ATP gamma S in isolated rat brain synaptosomes

The effects of ATP gamma S, a slowly hydrolyzable analogue of ATP, were investigated in the preparation of synaptosomes isolated from rat cerebral cortex. It was found that addition of [35S]ATP gamma S resulted in substantial magnesium-dependent incorporation of 35S into synaptosomal proteins which was prevented completely by ATP. The most prominently labeled polypeptides were those with apparent molecular weights of 100,000; 84,000; 74,000; 62,000; 55,000; 48,000; and 41,000. The rate and extent of thiophosphorylation were unaffected by addition of cAMP, veratridine or sodium fluoride. ATP gamma S at 50-100 microM had no effect on either uptake or release of gamma-aminobutyric acid (GABA) and dopamine; at a concentration of 1 mM it inhibited incorporation of dopamine by about 20%. This inhibition was also seen with 1 mM GTP, beta, gamma-methylene-adenosine 5'-triphosphate and adenylylimidodiphosphate, which suggests that the nucleotide triphosphates themselves, and not membrane protein phosphorylation, were responsible for the effect observed. It is concluded that ATP gamma S is an effective tool for studying the possible role of ATP released in synaptic transmission. The results obtained thus far suggest that neither extrasynaptosomal ATP nor phosphorylation of external proteins of the presynaptic membrane is sufficient for modulation of neurotransmitter uptake or release. They may, however, play a role in combination with other conditions.