The effect of metabolic substrate on mechanical activity and heat production in papillary muscle

Abstract

The heat production and isometric mechanical performance of isolated rabbit papillary muscles have been measured under varying metabolic conditions by including pyruvate (P), lactate (L), acetate (A), or glucose (G) at 10 mM concentration in the bathing medium. The resting rate of heat production was found to decrease with substrate in the order PALG, whereas the strength of isometric contraction decreased in the order PLAG. A method is presented for deriving the recovery heat production of isolated cardiac muscle from records of total heat production. When the recovery heat thus derived is normalized in terms of the mechanical output, a significant effect of metabolic substrate on the speed of oxidative metabolism is indicated. The substrates apparently caused the rate of recovery metabolism to decrease in the order PLAG.