Calcium is involved in the capsaicin-induced inhibition on neuronal excitability and analgesia. (A) whole-cell patch-clamp recording showed that in the absence of extracellular calcium, the ratio of action potential frequency was only partially inhibited in capsaicin-pretreated small DRG neurons. ***p < 0.001, versus the same group of neurons before capsaicin treatment (n = 30). (B, C) Behavior test showed that 50 μg capsaicin or 10 mM calcium or vehicle (n = 9) alone could not reduce the nociceptive response in the phase II of formalin test. However, the injection of a mixture of 50 μg capsaicin with 10 mM calcium (n = 7) could inhibit the reaction in the phase II (p < 0.001 for rats treated with capsaicin mixed with 10 mM calcium versus vehicle group, ANOVA). Data are shown as mean ± SEM. **p < 0.01, versus vehicle group.