Extracellular Action Potentials of Subepicardial Intact Cardiomyocytes of the Heart of Active and Hibernating Little Ground Squirrels Spermophilus pygmaeus

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Abstract

Hibernation is an important adaptive strategy for survival in adverse environmental conditions, including temperature reduction. The heart of hibernating animal species is quite resistant to cold-induced arrhythmia. However, the cellular basis of hibernating mechanisms has not been fully studied. One of the possible mechanisms of protection from cold-induced arrhythmias during hibernation is the remodeling of ion channels in cardiomyocytes, which can be accompanied by remodeling of the T-system. Therefore, the aim of this work was to compare the electrophysiological parameters of the heart of the little ground squirrel S. pygmaeus during the periods of activity and hibernation. To achieve this goal, extracellular action potentials (eAPs) were recorded. The eAPs of the ground squirrel heart are signals of two types: eAP1 from the sarcolemma areas free of the T-tubule openings, and eAP2 from the areas including the T-tubule openings. During the hibernation period statistically significant changes in the eAPprofiles are observed, manifested in a decrease in the amplitude of the second peak of eAP2, an increase in the duration of the decay to 90% (T90) in eAP1 and its shortening in eAP2. In addition, in hibernating ground squirrels, the profiles of both eAP types are accompanied by a significantly increased phase of afterhyperpolarization (AHP). Substantial changes during hibernation are also observed in the ratio of the eAP1 and eAP2 towards an increase in the number of eAP1. Similar changes in the ratio of different types of eAPs, shown by us for rats with type I diabetes mellitus, were associated with changes in the T-tubule system. However, preliminary results of studying ground squirrel hearts with confocal microscopy did not reveal visible differences in the organization of the T-system. This presumably indicates that hibernating ground squirrels have a considerably lower density of functional T-tubules due to a decrease in the density of ion channels in the T-system membrane.

About the authors

A. V Stepanov

Sechenov Institute of Evolutionary Physiology and Biochemistry of the Russian Academy of Sciences; St. Petersburg State Pediatric Medical University

Email: botanik2407@gmail.com
St. Petersburg, Russia

M. G Dobretsov

Sechenov Institute of Evolutionary Physiology and Biochemistry of the Russian Academy of Sciences

St. Petersburg, Russia

Yu. A Filippov

Sechenov Institute of Evolutionary Physiology and Biochemistry of the Russian Academy of Sciences

St. Petersburg, Russia

E. R Nikitina

Sechenov Institute of Evolutionary Physiology and Biochemistry of the Russian Academy of Sciences

St. Petersburg, Russia

K. S Bekshokov

Dagestan State University

Makhachkala, Russia

I. V Kubasov

Sechenov Institute of Evolutionary Physiology and Biochemistry of the Russian Academy of Sciences

St. Petersburg, Russia

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