P1- and P2-purinoceptor subtypes--an update.

It is suggested that neither the P1- nor the P2-purinoceptor forms a homogeneous group and that each can be separated into at least two subtypes. Biochemical, ligand binding and pharmacological studies clearly indicate that the P1-purinoceptor can be subdivided into the A1- and A2-subtypes. The recent development of antagonists, selective for the A1-subtype, supports this conclusion. Evidence for an A3-receptor also exists. On the basis of the rank order of potency of structural analogues of ATP and on the activity of antagonists, it is suggested that the P2-purinoceptor may be divided into the P2x- and P2y-subtypes. beta,gamma-methylene-L-ATP is a specific agonist at the P2x-subtype and ADP-beta-F a specific agonist at the P2y-subtype. Suramin acts as an antagonist at both subtypes, but reactive blue 2 appears to display selectivity for the P2y-purinoceptor. There is also evidence for P2t- and P2z-purinoceptors.