CONTRACTILE PROPERTIES OF RAT, RHESUS-MONKEY, AND HUMAN TYPE-I MUSCLE-FIBERS

It is well known that skeletal muscle intrinsic maximal shortening vel ocity is inversely related to species body mass. However, there is unc ertainty regarding the relationship between the contractile properties of muscle fibers obtained from commonly studied laboratory animals an d those obtained from humans. In this study we determined the contract ile properties of single chemically skinned fibers prepared from rat, rhesus monkey, and human soleus and gastrocnemius muscle samples under identical experimental conditions. All fibers used for analysis expre ssed type I myosin heavy chain as determined by sodium dodecyl sulfate -polyacrylamide gel electrophoresis. Allometric coefficients for type I fibers from each muscle indicated that there was little change in pe ak tension (force/fiber cross-sectional area) across species. In contr ast, both soleus and gastrocnemius type I fiber maximal unloaded short ening velocity (V-o), the y-intercept of the force-velocity relationsh ip (V-max), peak power per unit fiber length, and peak power normalize d for fiber length and cross-sectional area were all inversely related to species body mass. The present allometric coefficients for soleus fiber V-o (-0.18) and V-max (-0.11) are in good agreement with publish ed values for soleus fibers obtained from common laboratory and domest icated mammals. Taken together, these observations suggest that the V- o of slow fibers from quadrupeds and humans scale similarly and can be described by the same quantitative relationships. These findings have implications in the design and interpretation of experiments, especia lly those that use small laboratory mammals as a model of human muscle function.