Fig. 1.

A, Whole-cell voltage-clamp recordings obtained from cultured dorsal root ganglion and superior cervical ganglion neurons reveal a subpopulation of DRG cells that produce inward cationic currents when stimulated by heat in the noxious range. Averaged current temperature plots of noxious heat-sensitive DRG neurons (squares, n = 22), noxious heat-insensitive DRG neurons (triangles,n = 20), and SCG neurons (circles,n = 17). Inset shows recording from a noxious heat-sensitive DRG cell. Top and bottom traces are temperature and current recordings, respectively. Holding potential: −60 mV. B, Heat ramp from 37−52°C (1.75°C/sec) evokes specific heat-activated inward current that increases sharply above 45°C. C, Capsaicin superfusion (2 μm, 2 sec) to the same neuron as B also produces an inward current. D, Relationship between maximum amplitudes of currents evoked by the standard heat ramp stimulation (37−52°C, 1.75°C/sec) and subsequent capsaicin application (2 μm, 2 sec). Correlation coefficient,r² = 0.53.