Discrimination between UTP‐ and P2‐purinoceptor‐mediated depolarization of rat superior cervical ganglia by 4, 4′‐diisothiocyanatostilbene‐2, 2′‐disulphonate (DIDS) and uniblue A

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Abstract
1 Using a grease-gap recording technique we have investigated the effects of some antagonists of P2-purinoceptors on the depolarization of the rat isolated superior cervical ganglion evoked by 100 μMα, β-methylene-adenosine 5′-triphosphate (α, β-MeATP) or uridine 5′-triphosphate (UTP). The effects of the putative P2Z-purinoceptor antagonist, coomassie brilliant blue G, putative P2X-purinoceptor antagonist, 4, 4′-diisothiocyanatostilbene-2, 2′-disulphonate (DIDS) and uniblue A (an analogue of the P2Y- and P2X-purinoceptor antagonist reactive blue 2) were investigated. 2 At the highest concentration examined uniblue A (300 μM) depressed α, β-MeATP-induced depolarization and at 100 and 300 μM enhanced UTP-evoked depolarizations. Coomassie brilliant blue G (1 and 10 μM) did not affect depolarizations evoked by α, β-MeATP or UTP. Depolarizations evoked by potassium (5 mM) or muscarine (100 nM) were unaltered by either coomassie brilliant blue G or uniblue A. Uniblue A (100 and 300 μM) produced a concentration-dependent depression of hyperpolarizations evoked by adenosine (100 μM) whereas coomassie brilliant blue G at up to 10 μM, did not alter adenosine-induced hyperpolarizations. 3 DIDS (30 and 100 μM) did not alter adenosine-evoked hyperpolarizations, or depolarizations evoked by potassium or UTP. DIDS at 100 μM did not alter depolarizations evoked by muscarine. In contrast DIDS produced a concentration-dependent depression of α, β-MeATP-evoked depolarizations. 4 These results are consistent with the proposal that uniblue A and DIDS but not coomassie brilliant blue G are antagonists of P2-purinoceptors and that uniblue A is also an antagonist at P1 -purinoceptors present on the rat superior cervical ganglion. 5 The ability of uniblue A and DIDS to distinguish between depolarizations evoked by UTP and α, β-MeATP provides further justification for the proposal that these nucleotides activate separate receptors present on the rat superior cervical ganglion, i.e. pyrimidinoceptors and P2-purinoceptors respectively.

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