Size Principle of Striated Muscle Cells

Abstract

We have investigated the relationship between cross-sectional area (CSA) and maximum rate of oxygen consumption (VO2max, in nmol .mm-3 .s-1) of heart and skeletal muscle cells from different species. VO2max and CSA were determined for single muscle fibres of Xenopus laevis at 20°C and for cardiomyocytes in thin trabeculae dissected from the right ventricle of rats at 38°C. Succinate dehydrogenase activity was determined using a quantitative histochemical method to estimate VO2max in mammalian skeletal muscle fibres. Literature values of volume density of mitochondria were used to estimate VO2max in some mammalian cardiomyocytes. We found that an inverse relationship exists between VO2max (range 1.5 to 0.024 nmol . mm-3 . s-1) and cross-sectional area (0.0002 to 0.018 mm2, respectively): VO2max = constant/CSA, where the value of the constant equals 0.39±0.18 pmol . mm-1 .s-1 (mean ± S.D., n = 14). Such a relationship is predicted by a simple Hill-type model for oxygen diffusion in cilindrical cells, if it is assumed that muscle cells are evolved so that anoxic cores in muscle cells are prevented. This indicates that the product of endurance of muscle cells (which is proportional to VO2max) and force production (which is proportional to cross-sectional area) is limited by oxygen diffusion, and that adaptation of heart and skeletal muscle cells to increased workload is limited by the interstitial oxygen tension.