ABSTRACT
The term purinergic was coined 25 years ago by Burnstock (1) to explain the potential signaling role of A TP in noncholinergic, nonadrenergic transmission. Although the action of A TP on discrete cell surface receptors was recognized during subsequent years, it was not untill978 (2) that receptors activated by ATP or ADP (P2-purinoceptors, or P2 receptors) were differentiated from those activated by the ATP metabolite adenosine (Pr purinoceptors). P2 purinoceptors were further subdivided into two major groups: P2x-purinoceptors, which mediate vasoconstriction and smooth muscle contraction and were most potently activated by a,,B-methylene ATP (a,,B-meAT£), and P2y-purinoceptors, which promoted vasodilatation and smooth muscle relaxation and were potently activated by 2-methylthio-ATP (2MeSATP) (3). Additional Pz-purinoceptor subtypes have been subsequently proposed. For example, the stimulatory action of ADP on platelets was ascribed to a so-called P2rpurinoceptor at which ATP acts as an antagonist ( 4,5). A pore-forming ATP4-receptor was described on macrophages and mast cells and was termed the P2z-purinoceptor (6) (for
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