Acid increases inflammatory pain in rats: effect of local peripheral ASICs inhibitors

The purpose of this study was to assess the possible antinociceptive effect of the acid sensing ion channels (ASICs) inhibitors amiloride and benzamil after local peripheral administration in three models of inflammatory pain in rats. Reduction of pH, from 7.4 to 5.8 units, significantly increased the flinching/licking behavior induced by either 0.1% serotonin, 0.1% capsaicin or 0.5% formalin. Local peripheral ipsilateral, but not contralateral, injection of amiloride or benzamil significantly reduced nociceptive behaviors (flinching and licking/lifting) induced by serotonin, capsaicin or formalin in acidic conditions (pH 6.2). Interestingly, benzamil produced antinociception at low doses (0.001-0.1 microM/paw) while higher doses (1 microM/paw) did not affect capsaicin- or formalin-induced licking/lifting. Our data suggest that local peripheral inhibition of ASICs play an important role in inflammatory pain.