Energy turnover in hypoxic heart muscle.
In isolated rabbit papillary muscles at 20 degrees C, we studied the relationship between demand, supply, and utilisation of energy in hypoxia. Since shortage of energy is an important factor in loss of contractile performance following an hypoxic period, we tried to find a relationship between the loss of force production upon reoxygenation and the demand, supply, and utilisation of energy. Energy demand in hypoxia was defined as the -P turnover found in oxygen under further identical conditions. Energy supply in hypoxia was determined from lactate formation, using a P/lactate ratio of 1, while energy utilisation in hypoxia was obtained from the sum of: -P supply, the decrease of PCr and ATP, and the increase of AMP. Energy demand in hypoxia was varied by stimulating the hypoxic muscles at 0.2 Hz or not at all. For contracting hypoxic muscles energy supply by glycolysis was only 23% of energy demand. After 40 min of hypoxia force did only partially recover (78%) upon reoxygenation. For muscles at rest in hypoxia, force recovery was significantly (p less than 0.05) better (94% of control). However, energy supply was no more than 15% of the demand because supply was almost proportionally lower. It is concluded that the loss of force production upon reoxygenation is not related to the supply: demand ratio. By taking the integrated difference after 40 min of hypoxia between energy demand and utilisation, the energy deficit built up in hypoxia was estimated. In contracting muscle this was 2 times higher than in resting ones. It is suggested that a relationship could exist between the energy deficit and the loss of contractile performance upon reoxygenation. Experiments to test this idea are discussed.
Elzinga
G
G
Laboratory for Physiology, Free University, Amsterdam, The Netherlands.
Mast
F
F
Dietrich
D
D
D000818:Animals; D004734:Energy Metabolism / Q000502:physiology*; D066298:In Vitro Techniques; D007537:Isometric Contraction / Q000502:physiology; D007773:Lactates / Q000378:metabolism; D009200:Myocardial Contraction / Q000502:physiology*; D010100:Oxygen / Q000502:physiology*; D010210:Papillary Muscles / Q000502:physiology; D011817:Rabbits
D007773:Lactates; D010100:Oxygen