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Glycogen consumption in hypoxic rat cardiomyocytes.
1Department of Medical Physiology, University of Tromsø, Norway.
Canadian Journal of Physiology and Pharmacology
|April 1, 1992
Summary
Isolated rat heart cells under hypoxia showed minimal glycogen use, even with severe ATP depletion. This suggests glycogen stores are largely preserved, possibly due to hypercontracted cells limiting access.
Area of Science:
- Cardiovascular Physiology
- Cellular Metabolism
- Biochemistry
Background:
- Understanding cardiac energy metabolism during hypoxia is crucial for treating heart conditions.
- Glycogen serves as an important endogenous fuel source for the heart.
- Previous research indicated cyclic AMP levels are unaffected by hypoxia in myocytes.
Purpose of the Study:
- To investigate glycogen consumption in isolated adult rat myocytes under substrate-free, hypoxic conditions.
- To determine the factors limiting glycogenolysis during severe cellular energy depletion.
Main Methods:
- Isolated adult rat myocytes were incubated in hypoxic Krebs-Henseleit bicarbonate buffer without substrate.
- Measurements included glycogen content, adenosine triphosphate (ATP), adenosine monophosphate (AMP), and lactate.
- Experiments involved glucose supplementation and cyanide addition to assess enzyme activation.
Main Results:
- Minimal glycogen consumption (23%) was observed after 2 hours of hypoxia, despite an 89% reduction in ATP.
- Lactate accumulation did not inhibit glycolysis, as glucose supplementation maintained high energy phosphates.
- Increased AMP levels (induced by cyanide) did not enhance glycogen consumption, ruling out phosphorylase b inhibition.
Conclusions:
- Cardiac glycogen stores are significantly preserved during severe hypoxia and ATP depletion in isolated rat myocytes.
- The limited glycogenolysis is not due to lactate inhibition or impaired activation of glycogen phosphorylase.
- The majority of the remaining glycogen is likely inaccessible in hypercontracted myocytes.