Trezise D J, Bell N J, Khakh B S, Michel A D, Humphrey P A
Glaxo Institute of Applied Pharmacology, Department of Pharmacology, University of Cambridge, UK.
Eur J Pharmacol. 1994 Jul 11;259(3):295-300. doi: 10.1016/0014-2999(94)90656-4.
The antagonist properties of pyridoxal-5-phosphate, a synthesis precursor of pyridoxalphosphate-6-azophenyl-2',4'-disulphonic acid, were investigated on P2 purinoceptor-mediated responses of the rat isolated vagus nerve and vas deferens. In addition, the effect of this agent was studied on high affinity tritiated alpha,beta-methylene adenosine triphosphate (alpha,beta-meATP) binding to rat vas deferens membranes, thought to represent binding to functional P2x purinoceptors. In the rat vagus nerve, pyridoxal-5-phosphate (10(-5)-10(-4) M) produced concentration-related antagonism of depolarisation responses induced by alpha,beta-meATP, measured using an extracellular recording technique. In contrast, depolarisation responses to 5-hydroxytryptamine (5-HT) were unaffected by pyridoxal-5-phosphate. In the rat vas deferens, pyridoxal-5-phosphate (10(-5)-10(-4) M) antagonised contractile responses produced by alpha,beta-meATP while contractions to phenylephrine were unaffected. However, responses of the vagus nerve and the vas deferens to alpha,beta-meATP were not antagonised by pyridoxal hydrochloride (10(-4) M). Pyridoxal-5-phosphate competed for high affinity binding of [3H]alpha,beta-meATP to homogenised membranes of the rat vas deferens with a pKi estimate of 4.91 +/- 0.12 and a Hill slope of 0.80 +/- 0.03. Pyridoxal hydrochloride only competed for binding at concentrations in excess of 10(-4) M, yielding a pKi estimate of 3.21 +/- 0.04 and a Hill slope of 1.82 +/- 0.12. These findings indicate that pyridoxal-5-phosphate acts as a specific antagonist of P2 purinoceptors in the vagus nerve and vas deferens of the rat and that the phosphate moiety is required for activity.(ABSTRACT TRUNCATED AT 250 WORDS)
磷酸吡哆醛 -6- 偶氮苯 -2',4'- 二磺酸的合成前体磷酸吡哆醛的拮抗特性，在大鼠离体迷走神经和输精管的 P2 嘌呤受体介导的反应中进行了研究。此外，还研究了该试剂对与大鼠输精管膜高亲和力结合的氚化 α,β- 亚甲基三磷酸腺苷（α,β-meATP）的影响，这种结合被认为代表了与功能性 P2x 嘌呤受体的结合。在大鼠迷走神经中，采用细胞外记录技术测量，磷酸吡哆醛（10^(-5) - 10^(-4) M）对由 α,β-meATP 诱导去极化反应产生浓度相关的拮抗作用。相比之下，对 5- 羟色胺（5-HT）的去极化反应不受磷酸吡哆醛影响。在大鼠输精管中，磷酸吡哆醛（10^(-5) - 10^(-4) M）拮抗由 α,β-meATP 产生的收缩反应，而对去氧肾上腺素的收缩反应不受影响。然而，迷走神经和输精管对 α,β-meATP 的反应未被盐酸吡哆醛（10^(-4) M）拮抗。磷酸吡哆醛与 [3H]α,β-meATP 对大鼠输精管匀浆膜的高亲和力结合存在竞争，pKi 估计值为 4.91 ± 0.12，希尔系数为 0.80 ± 0.03。盐酸吡哆醛仅在浓度超过 10^(-4) M 时竞争结合，pKi 估计值为 3.21 ± 0.04，希尔系数为 1.82 ± 0.12。这些发现表明，磷酸吡哆醛在大鼠迷走神经和输精管中作为 P2 嘌呤受体的特异性拮抗剂起作用，且磷酸部分对活性是必需的。（摘要截短于 250 字）
