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

DiI-labeled colon sensory newtons were acutely dissociated from S1 rat dors al root ganglia (DRG) and studied using perforated whole cell patch-clamp t echniques. Forty-six percent (54/116) of labeled sensory neurons responded to capsaicin (10(-8)-10(-5) M) with an increase in inward current, which wa s a nonspecific cation conductance. Responses to capsaicin applied by puffe r ejection were dependent an dose, with a half-maximal response at 4.9 x 10 (-7) M; bath application was characterized by marked desensitization. Volta ge-gated Na+ currents in 23 of 30 DRG cells exhibited both TTX-sensitive an d TTX-resistant components. in these cells, capsaicin induced an inward cur rent in II of 17 cells tested. Of the cells containing only a TTX-sensitive component, none of six cells tested was sensitive to capsaicin. in all cel ls that responded to capsaicin with an increase in inward current, capsaici n abolished voltage-gated Na+ currents (n = 21). Capsazepine (10(-6) M) sig nificantly attenuated both the increase in inward current and the reduction in Na+ currents. Na+ currents were not significantly altered by adenosine, bradykinin, histamine, PGE(2), or serotonin at 10(-6) M and 10(-5) M. Thes e findings may have important implications for understanding both the irrit ant and analgesic properties of capsaicin.