Temperature sensitivity of Ca currents in chick sensory neurones

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.