Bactridine 2 effect in DRG neurons. Identification of NHE as a second target.

Bactridine 2 (Bact-2) is an antibacterial toxin from Tityus discrepans venom which modifies isoforms 1.2, 1.4 and 1.6 voltage-dependent sodium (Na) channels. Bactridine-induced Na outflow in Yersinia enterocolitica was blocked by amiloride, suggesting that Bact-2 effect was mediated by an amiloride sensitive sodium channel. In this study we show that Bact-2 increases also an outward rectifying current in rat dorsal root ganglia (DRG) sensory neurons; therefore, the nature of the outward rectifying currents was characterized and then the effect of Bact-2 on these currents was studied. These currents are enhanced by amiloride, are decreased by Na when an outward pH gradient is present and its reversal potential coincides with that of a Cl/H exchanger, suggesting that rectifying currents are produced by the electrogenic Cl/H exchanger modulated by the Na/H antiporter. Bact-2 also leads to an increase of the outward currents in a similar way to the produced by the inhibition of the Na/H exchanger. Additionally, the subsequent application of Bact-2 after blocking the Na/H exchanger does not produce any further effect, suggesting that Bact-2 modifies the outward current by modulating the activity of the Na/H exchanger. The effect of Bact-2 on pH regulation was determined using the pH indicator BCECF. The results show that the Na/H exchanger is blocked by amiloride and Na free solutions and is modulated by Bact-2 in a similar way as cariporide. This study validates that besides Na channels, Bact-2 modulates the activity of the Na/H exchanger.