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Antagonism by reactive blue 2 but not by brilliant blue G of extracellular ATP‐evoked responses in PC12 phaeochromocytoma cells

1 The effects of reactive blue 2 and brilliant blue G, which have been shown to block extracellular ATP‐evoked responses, were investigated to discover whether these compounds act as P2‐purinoceptor antagonists in PC12 phaeochromocytoma cells. 2 Reactive blue 2 (10 to 100 μm) suppressed the ATP‐stimulated dopamine secretion from PC12 cells in a dose‐dependent manner. The concentration‐response curve for ATP was shifted to the right and the maximal response was decreased by reactive blue (30 and 100 μm). Brilliant blue G (up to 100 μm) did not significantly affect the secretion. 3 Reactive blue 2 (10 to 100 μm) suppressed the ATP‐activated inward current recorded from the voltage‐clamped cells in a concentration‐dependent manner. Brilliant blue G (up to 100 μm) did not affect the current. 4 The results suggest that reactive blue 2 but not brilliant blue G is a P2‐purinoceptor antagonist in PC12 cells. The purinoceptors in these cells may be the same type as those involved in ATP‐evoked smooth muscle relaxation, judging from the antagonism by reactive blue 2.