Fig. 1.

Inhibition of ⁴⁵Ca uptake in rat DRG neurons after RTX pretreatment. A, Time course of the effect of RTX pretreatment on ⁴⁵Ca uptake. Cells were pretreated with 100 pm (□) and 250 pm (▪) resiniferatoxin and then challenged with 3 μm capsaicin. Two additional experiments yielded similar results. B, Comparison of dose–response curves for induction of ⁴⁵Ca uptake, [³H]RTX binding, and desensitization by RTX in rat DRG neurons. Data are expressed as uptake values above baseline for RTX-induced ⁴⁵Ca uptake (○) and as specifically bound [³H]RTX (▵) when binding was determined. Desensitization was defined as the difference (in dpm/well) in ⁴⁵Ca uptake between pretreated and control cells challenged with capsaicin. In the case of desensitization (▪), cells were pretreated with different concentrations of RTX for 6 hr and then challenged with 3 μm capsaicin. Points represent mean values from sets of eight determinations in a single experiment; error bars indicate SEM. The theoretical curves were calculated by fitting the measured values to the Hill equation. In the case of⁴⁵Ca uptake and desensitization, three additional experiments in each case yielded similar results. The dose–response curve for [³H]RTX binding is a single experiment, yielding binding parameters similar to those we found previously (Acs et al., 1996).