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

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Abstract
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 × 10−7M; 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 (10−6M) 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 10−6M and 10−5M. These findings may have important implications for understanding both the irritant and analgesic properties of capsaicin.