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 pituitar y cells and found that ATP produced a rapid biphasic cytosolic Ca2+ in crease in a dose-dependent manner in both rat pituitary gonadotropes a nd gonadotrope-derived alpha T3-1 cells. Removal of extracellular Ca2 only attenuated the plateau phase of ATP-induced intracellular Ca-2response and suramin (100 mu M), a P-2-purinoceptor antagonist reduced the ATP effect by 40 - 60%. Further studies revealed the following ra nk-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 an d UTP and these did not have additive effects. Together the data sugge st that the intracellular Ca2+ responses of gonadotropes and alpha T3- 1 cells to these nucleotides are mediated by a single class of recepto r pharmacologically characterized as the P-2U subtype. This is the fir st demonstration of functional ATP receptors in pituitary gonadotropes .