Introduction to the Special Issue on Purinergic Receptors.

In this Introduction to the series of papers that follow about purinergic receptors, there is a brief history of the discovery of purinergic signalling, the identity of purinoceptors and the current recognition of P1, P2X and P2Y subtypes. An account of key functions mediated by purinoceptors follows, including examples of both short-term and long-term (trophic) signalling and a table showing the selective agonists and antagonists for the purinoceptor subtypes. References to evolution and roles of purinoceptors in pathological conditions are also presented.