Characterization of purinergic receptors and receptor-channels expressed in anterior pituitary cells

Purinergic G protein-coupled receptors (P2YR) and ion-conducting receptor-c hannels (P2XR) are present in the pituitary. However, their identification, expression within pituitary cell subpopulations, and the ability to elevat e intracellular Ca2+ concentration ([Ca2+](i)) in response to ATP stimulati on were incompletely characterized. Here we show that mixed populations of rat anterior pituitary cells express messenger RNA transcripts for P2Y(2)R, P2X(2a)R, P2X(2b)R, P2X(3)R, P2X(4)R, and P2X(7)R. The transcripts and fun ctional P2Y(2)R were identified in lactotrophs and GH3 cells, but not in so matotrophs and gonadotrophs, and their activation by ATP led to an extracel lular Ca2+-independent rise in [Ca2+](i) in about 40% of cells tested. Lact otrophs and GH3 cells, but not somatotrophs, also express transcripts for P 2X(7)R, P2X(3)R, and P2X(4)R. Functional P2X(7)R were identified in 74% of lactotrophs, whereas 50% of these cells expressed P2X(3)R and 33% expressed PPX4R. Coexpression of these receptor subtypes in single lactotrophs was f requently observed. Purified somatotrophs expressed transcripts for P2X(2a) R and P2X(2b)R, and functional receptors were identified in somatotrophs an d Konadotrophs, but not in lactotrophs. Consistent with the cell-specific e xpression of transcripts for P2X(2)R and P2X(3)R, the expression of their f unctional heteromers was not evident in pituitary cells. Receptors differed in their capacities to elevate and sustain Ca2+ influx-dependent rise in [ Ca2+](i) during the prolonged ATP stimulation. These results indicate that the purinergic system of anterior pituitary is extremely complex and provid es an effective mechanism for generating a cell- and receptor-specific Ca2 signaling pattern in response to a common agonist.