Absence of metabolic rate allometry in an ex vivo model of mammalian skeletal muscle

Abstract

Within mammalian species, standard metabolic rate (SMR) increases disproportionately with body mass (Mb), such that the mass-specific SMR correlates negatively with Mb. This phenomenon can be explained in part by reduced cellular metabolic rates in larger species. To better understand the cause(s) of this cellular metabolic rate allometry we have used an ex vivo approach to isolate and identify potential contributors. Skeletal myoblasts from mammalian species ranging in Mb from 30g to over 300,000g were isolated and differentiated into myotubes in vitro. Oxygen consumption rates, citrate synthase (CS) activity, and lactate dehydrogenase (LDH) activity were measured in myotubes under standardized conditions. No correlation of any of these parameters was observed with species Mb, suggesting that there is no genetic contribution to between-species differences in cellular metabolic rates. Myotubes were incubated in serum from species ranging from 30g to 400,000g to determine whether between-species differences in the levels of metabolically important hormones might produce allometric trends in the cultured cells. However, there was no observed effect of serum donor Mb on any of the metabolic characteristics measured. Thus, there is no evidence for a relationship between skeletal muscle oxidative metabolism and Mb in an ex vivo model.