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

Article date: February 1995

By: Gerald P. Connolly, in Volume 114, Issue 3, pages 727-731

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.

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.

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.

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.

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.

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.

DOI: 10.1111/j.1476-5381.1995.tb17199.x

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