Abstract

The role of ATP on the modulation of noradrenaline release elicited by electrical stimulation (100 pulses/8 Hz) was studied in the prostatic portion of rat vas deferens preincubated with [³H]noradrenaline. In the presence of P1 antagonists, the nucleotides 2-methylthioadenosine-5′-triphosphate (2-MeSATP), 2-methylthioadenosine 5′-diphosphate (2-MeSADP), ADP, and ATP decreased electrically evoked tritium overflow up to 44%, with the following order of potency: 2-MeSATP > 2-MeSADP > ADP ≥ ATP. The P2Y antagonists reactive blue 2 (RB2) and 2-methylthioadenosine 5′-monophosphate (2-MeSAMP) increased, whereas the P2X antagonist pyridoxal-5′-phosphate-6-(2′-naphthylazo-6′-nitro-4′,8′-disulfonate) (PPNDS) decreased evoked tritium overflow. The inhibitory effect of 2-MeSATP was antagonized by RB2 (10 μM) and by 2-MeSAMP (10 μM) but not by the selective P2Y1 receptor antagonist 2′-deoxy-N⁶-methyladenosine 3′,5′-bisphosphate (MRS 2179; 10 μM). When, besides P1 receptors, inhibitory P2Y receptors were blocked with RB2, α,β-methyleneadenosine 5′-triphosphate (α,β-meATP), β,γ-imidoadenosine 5′-triphosphate (β,γ-imidoATP), β,γ-methyleneadenosine 5′-triphosphate (β,γ-meATP), 2-MeSATP, and ATP enhanced tritium overflow up to 140%, with the following order of potency: α,β-meATP > 2-MeSATP = ATP = β,γ-meATP ≥ β,γ-imidoATP. The facilitatory effects of α,β-MeATP and β,γ-imidoATP were prevented by PPNDS. Under the same conditions, apyrase attenuated, whereas the ectonucleotidase inhibitor 6-N,N-diethyl-d-β,γ-dibromomethylene 5′-triphosphate enhanced tritium overflow, an effect that was prevented by PPNDS. In the prostatic portion of the rat vas deferens, endogenous ATP exerts a dual and opposite modulation of noradrenaline release: an inhibition through activation of P2Y receptors with a pharmacological profile similar to that of the P2Y12 and P2Y13 receptors and a facilitation through activation of P2X receptors with a pharmacological profile similar to that of P2X1 and P2X3, or PX2/P2X3 receptors.