Overexpression of Cx43 and NF200 in the ground squirrel Citellus undulatus heart during the hibernation state

Objective: This study aims to quantify densities of the main cardiac ventricular gap junction protein Connexin43 (Cx43) and neuron marker Neurofilament200 (NF200) in the heart of hibernator ground squirrel (GS) Citellus undulatus. Methods: Fluorescence immunohistochemistry was performed on 16μm thick transmural sections of left ventricular free wall of summer active (SA, n=2), winter hibernating (WH, n=3), interbout arousal (IBA, n=3), and entrance into torpor (ET, n=2) GS. Densities were measured as protein area divided by tissue area (%). Results: Epicardial, mid‐myocardial, and endocardial Cx43 densities were significantly greater (P<0.05) in WH [13.5±0.6, 13.3±0.87, and 13.1±1.6] than in ET [9.7±0.5, 9.25±0.33, and 9.3±0.7], IBA [7.74±0.6 (epi) and 6.92±0.56 (mid)], and SA [8.8±0.5 (epi) and 9.1±0.9 (endo)]. NF200 density was higher in WH [2.3±0.1] than in ET [1.6±0.2], IBA [0.5±0.1], and SA [0.8±0.1]. Conclusions: Citellus undulatus can maintain proper heart rhythm during extreme hypothermic conditions through overexpression of Cx43 in ventricular myocytes. For the first time, autonomic innervation was found in endocardial ventricular tissue of a hibernating species through NF200 immunostaining. Overexpression of NF200 in WH indicates an important role of autonomic regulation in ventricular function during hibernation. (Support: Stanley and Lucy Lopata Endowment, RFFI05‐04‐48311)