PITUITARY ATP RECEPTORS - CHARACTERIZATION AND FUNCTIONAL LOCALIZATION TO GONADOTROPES

We have used real-time dynamic video imaging of Fura-2 fluorescence to study the acute effects of extracellular ATP on [Ca2+](i) in pituitary cells and found that ATP produced a rapid biphasic cytosolic Ca2+ increase in a dose-dependent manner in both rat pituitary gonadotropes and gonadotrope-derived alpha T3-1 cells. Removal of extracellular Ca2+ only attenuated the plateau phase of ATP-induced intracellular Ca-2+ response and suramin (100 mu M), a P-2-purinoceptor antagonist reduced the ATP effect by 40 - 60%. Further studies revealed the following rank-order of agonist potency in the Ca2+ response:- ATP = ADP = UTP > 2-methylthioATP >> beta,gamma-methylene ATP / alpha,beta-methylene ATP. Both homologous and heterologous desensitization occurred with ATP and UTP and these did not have additive effects. Together the data suggest that the intracellular Ca2+ responses of gonadotropes and alpha T3-1 cells to these nucleotides are mediated by a single class of receptor pharmacologically characterized as the P-2U subtype. This is the first demonstration of functional ATP receptors in pituitary gonadotropes.