COEXPRESSION OF HEAT-EVOKED AND CAPSAICIN-EVOKED INWARD CURRENTS IN ACUTELY DISSOCIATED RAT DORSAL-ROOT GANGLION NEURONS

Noxious heat is able to activate heat-sensitive nociceptors in the ski n very rapidly, but little is known about the mechanisms by which heat is transduced. We used the whole-cell patch-clamp technique to study the effects of noxious heat and capsaicin on freshly dissociated rat d orsal root ganglion neurons in vitro. Using temperatures between 41 de grees C and 53 degrees C, 8 of 19 small neurons (phi less than or equa l to 30 mu m) exhibited a heat evoked inward current. All heat-sensiti ve neurons tested were also capsaicin-sensitive. Moreover, the heat re sponse tended to be enhanced after capsaicin (360 +/- 150 pA versus 12 5 +/- 45 pA, P < 0.1, n = 7). Two of five heat-insensitive neurons wer e excited by capsaicin; both neurons developed a heat response after c apsaicin. Large neurons (phi > 30 mu m) did not respond to heat (0/7), and were not sensitive to capsaicin either. These findings indicate t hat heat stimuli may directly activate capsaicin-sensitive primary noc iceptive afferents. (C) 1997 Elsevier Science Ireland Ltd.