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Adaptive mechanisms of intracellular calcium homeostasis in mammalian hibernators

Shi Qiang Wang^1,2,*, Edward G. Lakatta², Heping Cheng² and Zeng Quan Zhou¹

¹ National Laboratory of Biomembrane and Membrane Biotechnology, College of Life Sciences, Peking University, Beijing 100871, China
² Laboratory of Cardiovascular Sciences, National Institute on Aging, NIH, Baltimore, MD 21224, USA

View larger version (12K): [in a new window]   Fig. 1. Low temperature increases intracellular free [Ca2+] markedly in resting cardiac myocytes from the rat, but not in those from the ground squirrel. The Ca2+ concentration was measured using the indo-1 fluorescence ratio as described in Wang and Zhou (1999b). Values are means ± S.E.M. (N=12 for rat, N=9 for ground squirrel; P<0.01 at 10°C).

View larger version (22K): [in a new window]   Fig. 2. General scheme of intracellular Ca2+ cycling. Ca2+ can enter the cell via Ca2+ channels and, in some situations, via the Na+—Ca2+ exchanger (NCX). Ca2+ can be released from sarcoplasmic/endoplasmic reticulum (SR/ER) via Ca2+-release channels, including ryanodine receptors and inositol (1,4,5)-trisphosphate receptors. Ca2+ is removed from the cytosol by SR/ER Ca2+-ATPase (SERCA), cytolemmal Ca2+-ATPase, Na+—Ca2+ exchange and the mitochondrial uniportor.

View larger version (10K): [in a new window]   Fig. 3. A comparison of action potential and contraction between cardiac myocytes from non-hibernating and hibernating ground squirrels. The arrow indicates the absence of the action potential plateau phase due to reduced L-type Ca2+ currents during hibernation. Note the larger contraction amplitude in the hibernating state (Wang et al., 1995).

View larger version (17K): [in a new window]   Fig. 4. Cardiac sarcoplasmic reticulum vesicles from winter-hibernating ground squirrels exhibit faster Ca2+ uptake than those from autumn, non-hibernating individuals. The graph shows the normalized change in [Ca2+] in 1 ml of reaction medium after addition of 1 mg SR protein. The initial uptake rates for non-hibernating and hibernating groups were 137±13 and 235±17 nmol Ca2+min-1mg-1 SR protein, respectively (Tang et al., 1995).