Pretreatment with capsaicin or RTX results in the desensitization of capsaicin-induced ⁴⁵Ca uptake in MC/9 cells. Cells were pretreated with different concentrations of capsaicin (○) or RTX (▪) for 6 hours and then were challenged with 3 μmol/L capsaicin for 30 minutes. For better comparison, the dose-response for RTX-induced desensitization on DRGs is also plotted (dotted line). Desensitization was defined as the difference (in dpm per well) in⁴⁵Ca uptake between pretreated and control cells when challenged with capsaicin. Points represent mean values from sets of five determinations in a single experiment; error bars indicate SEM. In both cases, at least three experiments yielded similar results. The theoretical curves were calculated by fitting the measured values to the Hill equation. The dose-response curve for RTX-induced desensitization on DRGs is a single experiment, yielding similar values to those found by us previously.10