Temperature-dependence of L-type Ca²⁺ current in ventricular cardiomyocytes of the Alaska blackfish (Dallia pectoralis)

Abstract

To lend insight into the overwintering strategy of the Alaska blackfish (Dallia pectoralis), we acclimated fish to 15 or 5 °C and then utilized whole-cell patch clamp to characterize the effects of thermal acclimation and acute temperature change on the density and kinetics of ventricular L-type Ca²⁺ current (I _Ca). Peak I _Ca density at 5 °C (−1.1 ± 0.1 pA pF⁻¹) was 1/8th that at 15 °C (−8.8 ± 0.6 pA pF⁻¹). However, alterations of the Ca²⁺- and voltage-dependent inactivation properties of L-type Ca²⁺ channels partially compensated against the decrease. The time constant tau (τ) for the kinetics of inactivation of I _Ca was ~4.5 times greater at 5 °C than at 15 °C, and the voltage for half-maximal inactivation was shifted from −23.3 ± 1.0 mV at 15 °C to −19.8 ± 1.2 mV at 5 °C. These modifications increase the open probability of the channel and culminate in an approximate doubling of the L-type Ca²⁺ window current, which contributes to approximately 15 % of the maximal Ca²⁺ conductance at 5 °C. Consequently, the charge density of I _Ca (Q _Ca) and the total Ca²⁺ transferred through the L-type Ca²⁺ channels (Δ[Ca²⁺]) were not as severely reduced at 5 °C as compared to peak I _Ca density. In combination, the results suggest that while the Alaska blackfish substantially down-regulates I _Ca with acclimation to low temperature, there is sufficient compensation in the kinetics of the L-type Ca²⁺ channel to support the level of cardiac performance required for the fish to remain active throughout the winter.