Increased connexin43 gap junction protein in hamster cardiomyocytes duringcold acclimatization and hibernation

Objective: The physiology of hibernation is characterized by dramatic reduc tions of heart rate, respiration, metabolism, blood pressure and body tempe rature and by resistance to ventricular fibrillation. Gap junctions in the heart provide low resistance pathways, facilitating electrical and metaboli c coupling between cardiac muscle cells for coordinated action of the heart and tissue homeostasis. The conductance of these junctions, and therefore their function, is likely to be affected by the physiological changes that take place during hibernation. Our objective was to quantitate gap junction protein levels in cold acclimatization, hibernation and arousal. Methods: We have used specific antibodies to connexins 43 and 40, in combination wit h confocal microscopy, to quantitatively analyze the expression of connexin protein in hamster (Mesocricetus auratus) left ventricles in four animal g roups: normal controls at euthermy, cold controls (cold-exposed animals tha t did not undergo hibernation), hibernating animals and animals aroused fro m hibernation for 2 h. Results: Connexin40 immunostaining was not detected in ventricular cardiomyocytes in any animal group but connexin43 was found in all groups. Connexin43 expression was significantly enhanced in hibernat ion and cold control ventricular cardiomyocytes. Total plaque area, numeric al density and plaque size were higher in the cold controls and hibernating hamsters compared to normal controls and animals aroused from hibernation. Conclusion: It is possible that the increased size and number of connexin4 3 gap junction plaques in the cold controls may represent a compensatory re sponse in order to maintain sufficient gap junction communication during ph ysiological conditions that would reduce conductance. These changes may rep resent a mechanism by which the hamster avoids ventricular fibrillation dur ing hibernation and arousal. (C) 2000 Elsevier Science B.V. All rights rese rved.