Characterization of P2x‐receptors in rabbit isolated ear artery

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Abstract
1 The isolated central ear artery of the rabbit contracts in response to adenosine 5′-triphosphate (ATP) and analogues, effects proposed to be mediated by stimulation of P2x-receptors. We have extended the characterization of the purinoceptor in this tissue by examining the effects of a series of receptor agonists. The study was designed in such a way as to avoid factors which normally limit attempts to classify receptors on the basis of agonist potency orders. 2 d-α,β-methylene ATP (d-α,β-meATP), d-β,γ-methylene ATP (d-β,γ-meATP), l-β,γ-methylene ATP (l-β,γ-meATP), 2-methylthio-d-ATP (2-MeSATP) and ATP produced concentration-related contractions of the ear artery with similar maximum responses, suggesting that they were full agonists. Selective desensitization of P2x-receptors abolished or greatly reduced responses to d-α,β-meATP, l-β,γ-meATP, d-β,γ-meATP and 2-MeSATP. Responses to ATP were inhibited by desensitization but a significant resistant component was still apparent. 3 d-α,β-meATP was the most potent agonist tested (pA50 6.47 ± 0.04) being 2138 times more potent than ATP and approximately 9 times more potent than l-β,γ-meATP. The agonist potency order was: d-α,β-meATP > l-β,γ-meATP > d-β,γ-meATP ≥ 2-MeSATP > ATP. This is generally consistent with the order proposed for P2x-receptors. The relative potencies of P2x-agonists in the rabbit ear artery show both similarities to and differences from data obtained in other smooth muscle preparations.

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