A PUTATIVE ROLE FOR EXTRACELLULAR ATP - FACILITATION OF COPPER-67 UPTAKE AND OF COPPER STIMULATION OF THE RELEASE OF LUTEINIZING-HORMONE-RELEASING HORMONE FROM MEDIAN-EMINENCE EXPLANTS

We have previously shown that extracellular copper stimulates the release of the luteinizing hormone-releasing hormone (LH-RH) from explants of the median eminence area (MEA), that chelated copper (Cu) but not ionic Cu is the active form of the metal, and that there is a direct correlation between the ligand specificity for Cu-67 uptake and Cu action. In this study, we examined the possibility that extracellular ATP can serve as a ligand facilitating Cu action on the LH-RH neuron. Hypothalamic slices or MEA explants of adult male rats were used. It was found that ATP facilitates Cu-67 uptake by hypothalamic slices when Cu:ATP molar ratio was 1:2000 but not 1:2. Keeping the [Cu] constant (150-mu-M) and varying [ATP], ATP facilitation of Cu stimulation of LH-RH release from MEA explants was found to be a saturable function of [ATP]; maximal facilitation occurred with 2.5 mM ATP. When the nucleotide phosphate specificity for facilitation of Cu action was assessed, ADP, ATP, alpha,beta-methylene-ATP (the non-hydrolyzable analogue of ATP) and GTP were equally effective, whereas AMP and adenosine were ineffective. These results indicate that extracellular ATP can facilitate Cu action on the LH-RH neuron and they are consistent with two mechanisms: (1) ATP facilitating Cu uptake and hence, Cu action and (2) ATP facilitating Cu action via an interaction with a purinergic receptor.