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 (hP2X1, hP2X3, hP2X4, and hP2X7), and two rat P2X receptor subtypes (rP2X2
and rP2X3), were stably expressed in 1321N1 human astrocytoma cells. Furthermore,
the rP2X2 and rP2X3 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 Ca2+ 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. Alphabeta-methylene
ATP (alphabeta-meATP), a putative P2X receptor-selective agonist, was found to exhibit
potent agonist activity only at the hP2X1, hP2X3 and rP2X3 receptor subtypes. Benzoylbenzoic
ATP (BzATP, 2' and 3' mixed isomers), which has been reported to act as a P2X7 receptor-selective
agonist, was least active at the rat and human P2X7 receptors, but was a potent (nM)
agonist at hP2X1, rP2X3 and hP2X3 receptors. These data comprise a systematic examination
of the functional pharmacology of P2X receptor activation.