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

Abstract

Summary To lend insight into the overwintering strategy of the Alaska blackfish (Dallia pectoralis), we acclimated fish to 15°C 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 culminated in an approximate doubling of the L-type Ca2+ window current, which contributed 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 Ca 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.

Cardiophysiological responses of the air-breathing Alaska blackfish to cold acclimation and chronic hypoxic submergence at 5°C

“…Fish were stunned by a sharp blow to the head, the spine was severed and the heart rapidly excised. The aortic bulb was cannulated and myocytes were isolated by retrograde perfusion of the heart with low-Na + solution containing (in mmol l −1 ): 100 NaCl, 10 KCl, 1.2 KH 2 PO 4 •2H 2 O, 4 MgSO 4 •7H 2 O, 50 taurine, 10 glucose and 10 Hepes at pH 6.9, supplemented with proteolytic enzymes (1.5 mg ml −1 collagenase type IA, 1 mg ml −1 trypsin type IX) and fatty acid-free bovine serum albumin (1.5 mg ml −1 ) for 30-35 min, as described previously in detail (Kubly and Stecyk, 2015;Vornanen, 1997). The ventricle was minced and triturated with a Pasteur pipette to obtain individual myocytes.…”

The temperature dependence of electrical excitability in fish hearts

“…In fish cardiac myocytes, the temperature dependence of I K1 density is weak (Q 10 =1.3-1.5) in comparison to that of I Kr density (Q 10 =2.3-3.2) (Vornanen et al, 2002a,b). The peak amplitude of the fish cardiac I Ca has a Q 10 value of ∼1.8 in rainbow trout cardiac myocytes (Shiels et al, 2000), but the peak amplitude of this current is much larger in the ventricular myocytes of the Alaska blackfish (Dallia pectoralis), especially at low temperatures (Kubly and Stecyk, 2015). Temperature-and voltage-dependent changes in the opening and closing kinetics of ion channels play a large role in thermal responses.…”

“…Temperature-and voltage-dependent changes in the opening and closing kinetics of ion channels play a large role in thermal responses. Temperature-induced changes in APD are probably largely due to temperature-dependent changes in the rate of I CaL inactivation (Shiels et al, 2000;Kubly and Stecyk, 2015).…”

“…It should be noted, however, that there are a few fish species that become inactive or dormant in winter, such as crucian carp (Carassius carassius), cunner (Tautogolabrus adspersus), annual killifish (Austrofundulus limnaeus) and ( perhaps) the air-breathing Alaska blackfish (Podrabsky and Hand, 1999;Vornanen et al, 2009;Costa et al, 2013;Kubly and Stecyk, 2015). These species do not need to compensate for reductions in temperature with changes in cardiac activity, which is reflected by the absence of positive compensation or even the reduction in ion current densities in the cold (i.e.…”

“…These species do not need to compensate for reductions in temperature with changes in cardiac activity, which is reflected by the absence of positive compensation or even the reduction in ion current densities in the cold (i.e. reverse thermal compensation) (Vornanen and Paajanen, 2004;Kubly and Stecyk, 2015).…”