Temperature sensitivity of Ca currents in chick sensory neurones

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Abstract
We have investigated the effects of temperature on the Ca currents of chick sensory neurones. Raising the temperature from 17 to 37°C, caused low-threshold (LVA, T) and high-threshold (HVA, L and N) Ca currents to show a marked amplitude increase and a drastic acceleration of their activation-inactivation gatings. Compared to HVA channels, the LVA type showed a weaker temperature sensitivity. Its averageQ 10 values were closer to those of other voltage-operated ion channels: 1.7 (permeability), 1.9 (activation) and 2.2 (inactivation). Alternatively, the activation kinetics and peak permeability of HVA Ca channels showed maximalQ 10 values of about 5 and 2.8, respectively. HVA channel deactivation was less sensitive to temperature (Q 10 1.8). Inactivation of these channels was slow and monoexponential between 17 and 22°C, but faster and double exponential above 30°C, uncovering a fast temperature-sensitive decaying phase. The size and rate of decay of this component decreased with increasing membrane depolarizations and persisted at holding potentials positive to −80 mV, suggesting the involvement of temperature-sensitive Ca-mediated processes in the mechanism of HVA channel inactivation. Our data are consistent with the view that heating from 17 to 37°C causes both an increased probability of Ca channels to open and a drastic acceleration of their activation-inactivation kinetics.