Pharmacological characterization of recombinant human and rat P2X receptor subtypes

ATP functions as a fast neurotransmitter through the specific activation of a family of ligand-gated ion channels termed P2X receptors. In this report, six distinct recombinant P2X receptor subtypes were pharmacologically characterized in a heterologous expression system devoid of endogenous P2 receptor activity, cDNAs encoding four human P2X receptor subtypes (hP2X(1), hP2X(3), hP2X(4), and hP2X(7)), and two rat P2X receptor subtypes (rP2X(2) and rP2X(3)), were stably expressed in 1321N1 human astrocytoma cells. Furthermore, the rP2X(2) and rP2X(3) receptor subtypes were co-expressed in these same cells to form heteromultimeric receptors. Pharmacological profiles were determined for each receptor subtype, based on the activity of putative P2 ligands to stimulate Ca(2+) influx. The observed potency and kinetics of each response was receptor subtype-specific and correlated with their respective electrophysiological properties. Each receptor subtype exhibited a distinct pharmacological profile, based on its respective sensitivity to nucleotide analogs, diadenosine polyphosphates and putative P2 receptor antagonists, alpha beta-methylene ATP (alpha beta-meATP), a putative P2X receptor-selective agonist, was found to exhibit potent agonist activity only at the hP2X(1), hP2X(3) and rP2X(3) receptor subtypes. Benzoylbenzoic ATP (BzATP, 2' and 3' mixed isomers), which has been reported to act as a P2X(7) receptor-selective agonist, was least active at the rat and human P2X(7) receptors, but was a potent (nM) agonist at hP2X(1), rP2X(3) and hP2X(3) receptors. These data comprise a systematic examination of the functional pharmacology of P2X receptor activation. (C) 1999 Elsevier Science B.V. All rights reserved.