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Hibernation and Cardiac Arrhythmias
A NEW STUDY OF HIBERNATING animals may provide insight into arrhythmia therapies. The findings were presented at a poster session at the 56th Annual Meeting of the Biophysical Society (BPS), in February. Lai-Hua Xie, PhD, assistant professor at NJMS, and his colleagues, in collaboration with Stephen Vatner, MD, director of the NJMS Cardiovascular Research Center, completed the research.
Hibernating animals, like bears and bats, can be aroused from their slumber by external stimuli, but woodchucks are "true hibernators," who can enter a profoundly altered physiological state. Their body temperature drops sharply and heart and respiration rates slow dramatically. Despite – or perhaps because of – these changes, hibernating animals have been found to be more resistant to cardiac arrhythmias and sudden cardiac death.
The research team examined muscle cells isolated in winter and in summer from woodchucks. Using a charge-coupled device (CCD) camera, the researchers monitored the release and uptake of calcium ions when the cells were activated. The team found that in winter woodchucks the myocyte sarcoplasmic reticulum – the membrane system in muscle cells that stores and releases calcium – had less spontaneous leakage of calcium, released more of it during excitation, and took it back up faster than that of summer woodchucks or non-hibernating animals. Xie says this is likely to generate a stronger contraction and faster relaxation, and most importantly, to prevent abnormal changes in the heart's electrical activities.
Xie explains the overall effect is a higher resistance to arrhythmia in woodchucks in winter. Understanding these cardiac adaptive mechanisms in hibernators may suggest new strategies to protect non-hibernating animals, especially humans, from fatal cardiac arrhythmias induced by hypothermic stresses and myocardial ischemia.