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

Abstract

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. 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. 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. 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. 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. 1995 British Pharmacological Society