Capsaicin sensitivity and voltage-gated sodium currents in colon sensory neurons from rat dorsal root ganglia.

DiI-labeled colon sensory neurons were acutely dissociated from S1 rat dorsal root ganglia (DRG) and studied using perforated whole cell patch-clamp techniques. Forty-six percent (54/116) of labeled sensory neurons responded to capsaicin (10-8- 10-5M) with an increase in inward current, which was a nonspecific cation conductance. Responses to capsaicin applied by puffer ejection were dependent on dose, with a half-maximal response at 4.9 × 10-7 M; bath application was characterized by marked desensitization. Voltage-gated Na+currents in 23 of 30 DRG cells exhibited both TTX-sensitive and TTX-resistant components. In these cells, capsaicin induced an inward current in 11 of 17 cells tested. Of the cells containing only a TTX-sensitive component, none of six cells tested was sensitive to capsaicin. In all cells that responded to capsaicin with an increase in inward current, capsaicin abolished voltage-gated Na+currents ( n = 21). Capsazepine (10-6 M) significantly attenuated both the increase in inward current and the reduction in Na+currents. Na+ currents were not significantly altered by adenosine, bradykinin, histamine, PGE2, or serotonin at 10-6 M and 10-5 M. These findings may have important implications for understanding both the irritant and analgesic properties of capsaicin.