Acidic pH decreases the deactivation rate of capsaicin-activated responses of rat TRPV1 channels expressed in HEK-293 cells. A double application protocol was used to investigate the effect of different pH's on the off rate of capsaicin. Two short applications of capsaicin (1 s) were interrupted by 1 to 5 second applications of either control external solution (pH 7.4) or acidic external (pH 5.5). A). Representative trace illustrating that the deactivation rates of both capsaicin applications are similar when the interpulse interval is at physiological pH. B) In contrast, when the interpulse interval is under acidic (pH 5.5) conditions, the deactivation rate of the initial application is substantially slower as illustrated by a representative trace. C) Comparison of the effect of external pH on the deactivation rates following the first capsaicin application. D) Comparison of the effect of external pH on the deactivation of the second capsaicin application. Data are the mean off rates (τ) ± SEM.