Resting metabolism of mouse papillary muscle

The aims of this study were to measure the resting metabolic rate of isolated mouse papillary muscles and to determine whether diffusive O2 supply is adequate to support the resting metabolism. Resting metabolism of left ventricular papillary muscles was measured in vitro (27 degrees C) using the myothermic technique. The rate of resting metabolism declined exponentially with time towards a steady value, with a time constant of 18+/-2 min (n=13). There was no alteration in isometric force output during this time. The magnitude of the resting metabolism, which depended inversely on muscle mass, more than doubled following a change in substrate from glucose to pyruvate and was increased 2.5-fold when the osmolarity of the bathing solution was increased by addition of 300 mM sucrose. Addition of 30 mM 2, 3-butanedione monoxime affected neither the time course of the decline in metabolic rate nor the eventual steady value. Analysis of the diffusive oxygen supply to the isolated preparation indicated that small papillary muscles (mass <1 mg), which have a very high resting metabolic rate early in an experiment, are unlikely to be adequately oxygenated.