Temperature-dependence of L-type Ca2+ current in ventricular cardiomyocytes of the Alaska blackfish (Dallia pectoralis)
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 (ICa). Peak ICa 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 ICa 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 ICa (QCa) 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 ICa density. In combination, the results suggest that while the Alaska blackfish substantially down-regulates ICa 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.