An ultrastructural investigation into the size dependency of contractility of isolated cardiac muscle.
The maximal stress (force per cross-sectional area), maximal rate of stress development, and cross-sectional area of 30 rabbit right ventricular papillary muscles were measured. Both mechanical parameters declined with increasing muscle size (the stress-area relation). Three large and three small muscles were fixed for electronmicroscopy. Stereological analyses of these six muscles were undertaken to test the hypothesis that the stress-area relation is caused by differences in the relative proportions of mitochondria and contractile matrix between muscles of large and small cross-sectional area. No difference in the proportion of these two cytoplasmic components was found. Other possible explanations underlying the stress-area relation are discussed.
D000818:Animals; D008297:Male; D008854:Microscopy, Electron; D008929:Mitochondria, Heart / Q000502:physiology; D009200:Myocardial Contraction; D010210:Papillary Muscles / Q000648:ultrastructure*; D011817:Rabbits; D013314:Stress, Mechanical