Differentiation by pyridoxal 5‐phosphate, PPADS and IsoPPADS between responses mediated by UTP and those evoked by α,β‐methylene‐ATP on rat sympathetic ganglia

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Abstract
1 The effect of pyridoxal 5-phosphate, and the 2′,4′ and 2′,5′-disulphonic acid isomers of 6-azophenyl-pyridoxal 5-phosphate (PPADS and IsoPPADS respectively) on depolarization of the rat superior cervical ganglion evoked by α,β-methylene-adenosine 5′-triphosphate (α,β-Me-ATP) and uridine 5′-triphosphate (UTP) were determined by a grease-gap recording technique. 2 Pyridoxal 5-phosphate (10–100 μm) and PPADS (10–100 μm) enhanced UTP- and depressed α,β-Me-ATP-evoked depolarizations but did not significantly alter depolarizations evoked by potassium or hyperpolarizations evoked by adenosine. IsoPPADS (10 μm) depressed α,β-Me-ATP-evoked depolarizations but did not alter depolarizations evoked by UTP. Depolarizations evoked by muscarine were depressed by IsoPPADS but not by pyridoxal 5-phosphate. 3 It is concluded that pyridoxal 5-phosphate, PPADS and IsoPPADS are antagonists at P2X-purinoceptors but not at the receptors that mediate UTP-evoked depolarization of the rat superior cervical ganglion. These observations substantiate the recent proposal that the rat superior cervical ganglia possess distinct receptors for purine and pyrimidine 5′-nucleotides, i.e. P2X-purinoceptors and pyrimidinoceptors respectively.

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