Figure 3.

Noise associated with opening of heat-activated ion channels. (A) Examples of cell-attached patch-clamp recordings of the responses of a heat-insensitive neuron (top recording) and a heat-sensitive neuron (bottom recording) to temperature steps. Patch pipette contained only 154 mM NaCl/10 mM Hepes to maximize current through heat-sensitive ion channels and was held at 0 mV. Heat-sensitive currents through channels outside the patch were prevented by bathing the rest of the cell in solution free of permeant ions (154 mM N-methyl glucamine/10 mM Hepes). (B) Power spectrum of cell-attached current activated by a temperature step to 49°C. For each experiment, 10 consecutive traces (16,384 samples per trace at 10 kHz; filtered at 4 kHz) were acquired, first at room temperature then at 49°C, and the power spectra were calculated. Heat-induced power spectrum (points) was calculated as the difference between the two spectra. Power spectrum fitted with the sum of two Lorentzian functions (sum shown as a solid line; component spectra as a dashed line) with half-power frequencies as shown, corresponding to time constants of 17 ms and 0.49 ms (V.V., P.C., and P.A.M., unpublished data).