The Influence of Hibernation on Electrical Activity and Potassium Currents in Myocardium of Long-Tailed Ground Squirrel

Hibernating mammals are capable of reducing the temperature of their bodies down to 0°C. During this process, their heart is highly resistant to the occurrence of arrhythmias caused by temperature fall. In this research we have for the first-time studied potassium currents in the myocardium of a hibernating mammal on the example of long-tailed ground squirrel (Citellus undulatus) and its change upon hibernation. Using patch clamp method, we studied transient outward current I_to and background inward rectifier current I_K1 in isolated ventricular and atrial myocytes from summer (active) and winter (hibernating) ground squirrels. The study revealed, that at room temperature and at positive holding potentials peak amplitude of I_to in cardiomyocytes from hibernating group of animals is lower than that of the summer group. The downregulation of I_to upon hibernation was more pronounced in ventricular myocardium in comparison to that in atrial. Background inward rectifier current I_K1 was enhanced in ventricular myocardium of winter group of animals, upon the adaptation to hibernation. In atrial myocardium there were no statistically significant differences of I_K1 between the two groups. We also recorded action potentials in isolated ventricular cardiomyocytes. The duration of action potentials at the levels of 50 and 90% repolarization did not differ between the groups, we also did not find significant differences in maximum upstroke velocity and in the level of resting membrane potential. Taken together, the revealed differences in the amplitude of I_to and I_K1 between active and hibernating ground squirrels can serve as mechanisms increasing the duration of refractory period and to maintaining the level of resting membrane potential at low temperatures.