Some problems of cardiac energetics.
Special problems of the aerobic metabolism in the cardiac muscle cell as an energy producing and energy consuming system are discussed and demonstrated with some experimental results using superfused resting and working guinea-pig atria as an energetic model: 1. Influence on resting O2 uptake: a) Free fatty acids (FFA) increase the O2 uptake rate to approximately 20% compared with glucose oxidation. This can be explained as a compensating effect due to the 9.7% lower combustion value for 1 mol O2 of C16-FFA and the 10.7% lower P/O-ratio related to glucose oxidation. b) K+-depolarization increases the O2 uptake b.1. between 15 and 65 mmol/l KCl from 110 to 200% without activation of the actomyosin system. This effect is Ca++ dependent and is not observed in Ca++ free solution and can be inhibited completely by nifedipine. The enhanced O2 uptake rate due to K+-depolarization is not connected with an improved state of the energy quotient (ATP/ADP+AMP) indicating a lowering of the energy coupling. b.2. between 100 and 250 mmol/l KCl from 220 to approximately 350%, not influenced by nifedipine and connected with activation of the actomyosin system at low Na+ and/or high external Ca++ (contracture). 2. Stretching of resting atria up to 10 mN tension does not increase the O2 uptake rate. The 'Feng' effect could not be confirmed. 3. a) The 'Frank-Starling' effect can be observed between 2.5 and 10 mN preload with increase of contractile work/beat connected with an enhancement of O2 uptake rate to a lower percentage. At the maximum of the 'Frank-Starling' effect the highest efficiency of contractile work can be observed. With increasing beat rate this maximum is shifted to a lower preload. b) The auxotonic contractile work measured by a calibrated spring blade allows the calculation of the 'internal work' and the 'external contractile work'/beat in mm X mN. The total energy of the activated actomyosin system (total work) is stored by the displacement of the spring blade due to the constant of the spring blade, the preload (tension) and the afterload (force). The 'internal work' will be transformed into ATP dependent heat and force equal to the preload tension. The same ATP dependent energy from O2 uptake is transformed at the same beat rate and the same preload a) with the isometric type of auxotonic contraction into high force and very low internal and low external work.(ABSTRACT TRUNCATED AT 400 WORDS)
D000818:Animals; D004734:Energy Metabolism; D005230:Fatty Acids, Nonesterified / Q000378:metabolism; D006168:Guinea Pigs; D009200:Myocardial Contraction; D009206:Myocardium / Q000378:metabolism*; D010101:Oxygen Consumption
D005230:Fatty Acids, Nonesterified