Figure 9.

Membrane receptors for extracellular adenosine and ATP. (A) The P1 family of receptors for extracellular adenosine are G protein-coupled receptors (S–S; disulphide bond). (B) The P2X family of receptors are ligand-gated ion channels (S–S; disulphide bond; M1 and M2, transmembrane domains), and (C) the P2Y family are G protein-coupled receptors (S–S; disulphide bond). [(A) Modified from Ralevic and Burnstock (1998), reproduced with permission from the American Society for Pharmacology and Experimental Therapeutics; (B) from Brake et al. (1994), reproduced with permission from Nature; (C) modified from Barnard et al. (1994), reproduced with permission from Elsevier.]