The antagonist trinitrophenyl‐ATP reveals co‐existence of distinct P2X receptor channels in rat nodose neurones

1 Whole‐cell recordings were made from rat nodose ganglion neurones in culture and from human embryonic kidney (HEK293) cells stably transfected to express P2X 2 , P2X 3 or both receptor subunits. We examined the blocking actions of 2′,3′‐ O‐ trinitrophenyl‐ATP (TNP‐ATP) on currents evoked by the agonists ATP and α,β‐methylene ATP. 2 In cells expressing only P2X 2 or P2X 3 receptor subunits, the inhibition by TNP‐ATP was fitted by a single binding site model with half‐maximal concentrations of about 3 μM and 3 nM, respectively. In cells expressing both P2X 2 and P2X 3 receptor subunits, currents showed little or no desensitization, thus excluding contributions from homomeric P2X 3 receptors. When α,β‐methylene ATP was the agonist (activating heteromeric P2X 2 / 3 receptors), the inhibition by TNP‐ATP conformed to a single binding site (half‐maximal concentration about 3 nM). When ATP (30 μM) was the agonist, activating both heteromeric P2X 2 / 3 as well as homomeric P2X 2 receptors, the inhibition curve was biphasic (half‐maximal concentrations about 3 nM and 3 μM); the proportion of high affinity sites in all six cells tested was about 40 %. 3 In nodose ganglion neurones, the inhibition by TNP‐ATP of currents evoked by ATP (30 μM) was also clearly biphasic. In this case, individual neurones showed more variability in the proportion of high and low affinity sites for TNP‐ATP. 4 We conclude that more than one form of multimeric P2X receptor channels are functionally expressed on the cell bodies of individual nodose ganglion neurones. On the basis of sensitivity to TNP‐ATP, and other properties, one of these may correspond to the homomeric P2X 2 receptor and the other(s) to heteromeric P2X 2 / 3 receptors.