Figure 9. Adaptation of the cold- and menthol-activated current: time course, Ca²⁺ dependence and shift in temperature sensitivity.

Ai, time course of adaptation on cooling and the effect of removing extracellular Ca²⁺. Three pulses to 12 °C were applied, separated by 5 min, the second one (black) being in Ca²⁺-free extracellular solution and the first and third (grey) in normal [Ca²⁺]. Extracellular [Mg²⁺] was raised to 10 mm throughout. Aii, the effect on adaptation time course of including 10 mm BAPTA in the pipette solution, recorded in two different neurones in standard extracellular solution. The control recording was in the perforated-patch configuration and was chosen because its adaptation time constant (69 s) was close to the mean for all perforated-patch recordings (71.5 s). Currents are normalised; peak currents were ≈200 pA (BAPTA) and ≈500 pA (control). B, shift in the temperature sensitivity of the cold-activated current during successive falling and rising temperature ramps, in standard extracellular solution; i, raw currents and temperature stimulus, and ii, current-temperature relationship. Falling temperature ramps are shown in grey in ii, and rising ramps in black; the two pairs of ramps are marked a and b for easy identification. C, effect of cooling pulses of duration 10, 20 and 40 s on the temperature dependence of the cold-activated current, measured during rising ramps (a-c) following each cold pulse, in standard extracellular solution. i, raw currents; ii, current-temperature relationship, showing only currents during the rising ramps a-c. Holding potential was −60 mV in A-C.