The Effect of Regional Myocardial Heterogeneity on the Economy of Isometric Relaxation
This chapter is directed at clarifying the relationship between regional myocardial heterogeneity and the economy of contraction and relaxation . When heart muscle contracts and relaxes isometrically, there is considerable internal shortening and lengthening during the rise and fall of tension development . In-skeletal muscle, under those conditions where active muscle shortens and lengthens, the energetic cost of shortening is greater than that of lengthening [3–6]. Thus the economy of contraction is less than that of relaxation. If heart muscle is like skeletal muscle, one would expect the economy of relaxation to be greater than that of contraction. Inhomogeneity adds another dimension to this problem. Inhomogeneity is present in normal hearts and abounds under pathological conditions. In normal hearts there are geometric (apex to base) [7–10] and isoenzymic [11–16] differences. In the presence of regional ischemia, the stunned portion of the heart is much weaker than the nonstunned portion [17, 18]. When an infarct occurs, the noninfarcted remainder of heart may hypertrophy with the extent of the hypertrophic response being different in the various areas [19–22]. This heterogeneity results in a functional difference in myocytes or sarcomeres, which are in series with each other. How these differences affect the predicted increase in economy of isometric relaxation in contrast to contraction is the focus of this chapter.
KeywordsPapillary Muscle Rabbit Heart Relaxation Phase Initial Heat Ventricular Papillary Muscle
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- 1.Alpert NR, Mulieri LA, Litten RZ (1983). Isoenzyme contribution to economy of contraction and relaxation in normal and hypertrophied hearts. In Jacob R, Gulch RW, Kissling G (eds): Cardiac Adaptation to Hemodynamic Overload and Stress. Dr. D. Steinkopff Verlag, Damstadt pp 147–157.CrossRefGoogle Scholar
- 2.Kreuger JW, Pollack GH (1975). Myocardial sarcomere dynamics during isometric contraction. J Physiol 251: 627–643.Google Scholar
- 6.Curtin N, Davies RE (1975). Very high tension with very little ATP breakdown by active skeletal muscle. J Mechanochem Cell Mot 3: 147–154.Google Scholar
- 15.Schiaffino S, Gorza L, Sartore S (1983). Distribution of myosin types in normal and hypertrophic hearts: An immunocytochemical approach. In Alpert NR (ed): Myocardial Hypertrophy and Failure. New York Raven Press, pp 149–166.Google Scholar
- 20.Turek Z, Granthner M, Kubat K, et al (1973). Arterial blood gases, muscle fiber diameter and intercapillary distance in cardiac hypertrophy of rats with an old myocardial infarction. Pfluegers Arch 376: 209–215.Google Scholar
- 29.Alpert NR, Mulieri LA (1982). Increased myothermal economy of isometric force generation in compensated cardiac hypertrophy induced by pulmonary artery constriction in the rabbit: A characterization of heat liberation in normal and hypertrophied right ventricular papillary muscles. Circ Res 50: 491–500.PubMedGoogle Scholar
- 31.Flitney GW, Hirst DG, Jones DA (1976). Effects of temperature and velocity of stretch on the maximum tension borne by the sarcomeres in contracting muscle. J Physiol 256: 127–128.Google Scholar