Intracellular TH9402 measurement and association with depletion efficacy (N = 6). Data from 3 experiments (Exp's VII-IX) using 2 different TH9402 concentrations (5.0 and 7.5 μM) are summarized. (A) Course of intracellular TH9402 during the depletion process. *In one experiment no sample was available for the post–light exposure analysis for either condition (N = 4). Residual TH9402 concentrations are minimal and just higher than the background of the untreated control (N = 3). (B) The depletion efficacy (measured by the depletion index) against the original stimulator but not against the third party was positively correlated with the residual dye concentration after extrusion (directly before light exposure). The correlation coefficients and P values of the linear regression analysis are presented. **Statistically significant P value.