Full sensitivity of P2times2 purinoceptor to ATP revealed by changing extracellular pH

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Abstract
A full pharmacological characterization was carried out on a recombinant ATP-gated ion channel (P2times2 purinoceptor) expressed in Xenopus oocytes. This slowly-desensitizing neuronal P2times2 purinoceptor, activated by ATP (EC50 = 4.6 ± 1 μm at pH 7.4; n 4), showed the agonist potency order: ATP ≥ 2- MeSATP = ATPγS ≥ ATPαS < < Bz-ATP. The receptor affinity for ATP was enhanced 5–10 fold by acidifying the bathing solution (to pH 6.5) but was diminished 4–5 fold in an alkaline solution (pH 8.0). The maximum activity of P2times2 purinoceptors and the activity order of a series of nucleotides were unaltered by changing extracellular pH. Interestingly, ATP sensitivity at a recombinant P2Y1, purinoceptor remained unaltered with changing extracellular pH. These results indicate that acidotic conditions in the synaptic cleft could strengthen purinergic transmission at neuronal P2times2 purinoceptors.