Functional ATP receptors in rat anterior pituitary cells

The effects ofATP and other nucleotides on the cytosolicCa²⁺ concentration([Ca²⁺]_i)of single immunocytochemically typed anterior pituitary (AP) cells havebeen studied. ATP increased[Ca²⁺]_iin a large percentage (60-88%) of all five AP cell types:lactotropes, somatotropes, corticotropes, gonadotropes, andthyrotropes. Additivity experiments suggest the presence of at leasttwo different receptors, one accepting both ATP and UTP (U receptor),producing Ca²⁺ release from theintracellular stores, and the other preferring ATP (A receptor),producing Ca²⁺ (andMn²⁺) entry. The characteristicsof the U and A receptors were consistent with those ofP2Y₂ andP2X₂, respectively, and theirdistribution in the different AP cell types was not homogeneous. Thepresence of other ATP receptors suchP2Y₁ orP2X₂/P2X₃heteropolymers in a small fraction of the cells cannot be excluded.Thus functional ionophoric P2X receptors, which are typical of neuraltissue, are also present in the pituitary gland and could contribute to regulation of the gland's function.