Key result
Cardiomyocytes from ground squirrels maintained better intracellular Ca2+ homeostasis than rat cells through an elevated threshold for Ca2+ entry, suppressed sarcoplasmic reticulum Ca2+ leak, and accelerated cytosolic Ca2+ removal.
Cardiomyocytes from hibernating ground squirrels demonstrate adaptive mechanisms for Ca2+ homeostasis, including an elevated ICa threshold, suppressed SR Ca2+ leak, and accelerated Ca2+ removal, providing insights into cellular resistance against hypothermia and hypoxia.
Heart tissues from hibernating mammals, such as ground squirrels, are able to endure hypothermia, hypoxia and other extreme insulting factors that are fatal for human and nonhibernating mammals. This study was designed to understand adaptive mechanisms involved in intracellular Ca(2+) homeostasis in cardiomyocytes from the mammalian hibernator, ground squirrel, compared to rat. Electrophysiological and confocal imaging experiments showed that the voltage-dependence of L-type Ca(2+) current (I(Ca)) was shifted to higher potentials in ventricular myocytes from ground squirrels vs. rats. The elevated threshold of I(Ca) did not compromise the Ca(2+)-induced Ca(2+) release, because a higher depolarization rate and a longer duration of action potential compensated the voltage shift of I(Ca). Both the caffeine-sensitive and caffeine-resistant components of cytosolic Ca(2+) removal were more rapid in ground squirrels. Ca(2+) sparks in ground squirrels exhibited larger amplitude/size and much lower frequency than in rats. Due to the high I(Ca) threshold, low SR Ca(2+) leak and rapid cytosolic Ca(2+) clearance, heart cells from ground squirrels exhibited better capability in maintaining intracellular Ca(2+) homeostasis than those from rats and other nonhibernating mammals. These findings not only reveal adaptive mechanisms of hibernation, but also provide novel strategies against Ca(2+) overload-related heart diseases.
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Li et al. (2011) studied Intracellular Ca2+ homeostasis (Hibernation adaptation). Ground squirrel cardiomyocytes vs. Rat cardiomyocytes was evaluated on Intracellular Ca2+ homeostasis and Ca2+ cycling characteristics. Cardiomyocytes from ground squirrels maintained better intracellular Ca2+ homeostasis than rat cells through an elevated threshold for Ca2+ entry, suppressed sarcoplasmic reticulum Ca2+ leak, and accelerated cytosolic Ca2+ removal.
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