The activity of both myocardial ouabain-sensitive (Na+ + K+)-ATPase and ouabain-insensitive Mg2+-ATPase is reduced in the hearts of winter-hibernating ground squirrels compared to the activity in the hearts of awake-active animals sacrificed during the summer. (Na+ + K+)-ATPase preparations from the nonhibernating animals show nonlinear Arrhenius kinetics, with a marked increase in the Arrhenius activation energy (Ea) below 16°C. During hibernation this pattern of temperature dependence probably does not change significantly, but the level of enzyme activity below 16°C is now too low to measure with confidence. Conversely, even the reduced level of myocardial Mg2+-ATPase from the hearts of animals killed during hibernation continues to display the linear Arrhenius kinetics that were observed in these myocardial preparations from active summer animals. Biophysical studies of the whole myocardial membrane preparations by differential scanning calorimetry and examination of the total lipid extract from these membranes by electron spin resonance spectroscopy after labeling of the lipids with 16 NS suggest that the myocardial membrane is in a more fluid state when the animals are in hibernation. However, only a small percentage of the lipids of the membranes is involved in the thermal transitions observed, and the lack of coincidence of the temperature for these transitions and the parameters of activation energy for both myocardial adenosinetriphosphatases indicates that the activities of (Na+ + K+)-ATPase and Mg2+-ATPase are insulated against this change in lipid structure - possibly by a domain of boundary lipids possessing thermal properties different from those of the bulk phase. During hibernation there is a significant increase in the 182 (ω)6 fatty acid (linoleic) content of myocardial membranes.
|Number of pages||7|
|Publication status||Published - 1 Dec 1980|
ASJC Scopus subject areas
- Molecular Medicine