Expression and function of P2X purinoceptors in rat histaminergic neurons

The pharmacology of ATP responses and the expression pattern of seven known subunits of the P2X receptor were investigated in individual histaminergic neurons of the tuberomamillary nucleus (TM). ATP (3–1000 μ M ) evoked fast non‐desensitizing inward currents in TM neurons. 2‐methylthioATP (2MeSATP) displayed the same efficacy but a lower potency, EC 50 s 84 μ M versus 48 μ M , when compared with ATP. Adenosine‐diphosphate (ADP), uridine‐triphosphate (UTP) and alpha beta methylene‐ATP (αβ‐meATP) were inactive. ATP‐mediated whole cell currents were potentiated by acidification of the recording solution (pH 7.5 and 6.6 were compared). Single‐cell RT–PCR (scRT–PCR) analysis revealed that the P2X 2 receptor is expressed in all PCR‐positive neurons. Each of the P2X 1 , P2X 3 , P2X 4 , P2X 5 and P2X 6 mRNAs were detected in less than 35% of the cells. Suramin antagonized ATP responses with an IC 50 of 4.2 μ M and pyridoxalphosphate‐6‐azophenyl‐2′,4′‐disulphonic acid (PPADS, 1 μ M ) reduced ATP responses to 43% of control, when antagonists were pre‐applied 90s before the agonist. Cibacron blue (3 μ M ) given together with ATP potentiated control responses by 67%, but inhibited it to 10% after pre‐application. 2′,3′‐O‐(2,4,6‐Trinitrophenyl) adenosine 5′‐triphosphate (TNP–ATP) antagonized ATP responses with an IC 50 of 7 μ M . Pharmacological properties of ATP responses together with scRT–PCR data suggest that P2X 2 is the major purinoceptor on the soma of TM neurons, however the presence of heteromeric P2X 2/5 receptors in some neurons cannot be excluded.British Journal of Pharmacology (2003) 138 , 1013–1019. doi: 10.1038/sj.bjp.0705144