FUNCTIONAL ATP RECEPTORS IN RAT ANTERIOR-PITUITARY-CELLS

The effects of ATP and other nucleotides on the cytosolic Ca2+ concent ration ([Ca2+](i)) of single immunocytochemically typed anterior pitui tary (AP) cells have been studied. ATP increased [Ca2+](i) in a large percentage (60-88%) of all five AP cell types: lactotropes, somatotrop es, corticotropes, gonadotropes, and thyrotropes. Additivity experimen ts suggest the presence of at least two different receptors, one accep ting both ATP and UTP (U receptor), producing Ca2+ release from the in tracellular stores, and the other preferring ATP (A receptor), produci ng Ca2+ (and Mn2+) entry. The characteristics of the U and A receptors were consistent with those of P2Y(2) and P2X(2), respectively, and th eir distribution in the different AP cell types was not homogeneous. T he presence of other ATP receptors such P2Y(1) or P2X(2)/P2X(3) hetero polymers in a small fraction of the cells cannot be excluded. Thus fun ctional ionophoric P2X receptors, which are typical of neural tissue, are also present in the pituitary gland and could contribute to regula tion of the gland's function.