Identification of regions of the P2X7receptor that contribute to human and rat species differences in antagonist effects

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Abstract
Background and purpose: Several P2X7receptor antagonists are allosteric inhibitors and exhibit species difference in potency. Furthermore,N2‐(3,4‐difluorophenyl)‐N1‐(2‐methyl‐5‐(1‐piperazinylmethyl)phenyl)glycinamide dihydrochloride (GW791343) exhibits negative allosteric effects at the human P2X7receptor but is a positive allosteric modulator of the rat P2X7receptor. In this study we have identified several regions of the P2X7receptor that contribute to the species differences in antagonist effects.Experimental approach: Chimeric human‐rat P2X7receptors were constructed with regions of the rat receptor being inserted into the human receptor. Antagonist effects at these receptors were measured in ethidium accumulation and radioligand binding studies.Key results: Exchanging regions of the P2X7receptor close to transmembrane domain 1 modified the effects of KN62, 4‐(4‐fluorophenyl)‐2‐(4‐methylsulphinylphenyl)‐5‐(4‐pyridyl)1H‐imidazole (SB203580) and GW791343. Further studies, in which single amino acids were exchanged, identified amino acid 95 as being primarily responsible for the differential allosteric effects of GW791343 and, to varying degrees, the species differences in potency of SB203580 and KN62. The species selectivity of pyridoxalphosphate‐6‐azophenyl‐2′,4′‐disulphonic acid was affected by multiple regions of the receptor, with potency being particularly affected by the amino acid 126 but not by amino acid 95. A further region of the rat receptor (amino acids 154–183) was identified that, when inserted into the corresponding position in the human receptor, increased ATP potency 10‐fold.Conclusions: This study has identified several key residues responsible for the species differences in antagonist effects at the P2X7receptor and also identified a further region of the P2X7receptor that can significantly affect agonist potency at the P2X7receptor.British Journal of Pharmacology(2008)155, 738–751; doi:10.1038/bjp.2008.306; published online 28 July 2008