Factors affecting the metabolism of resting rabbit papillary muscle

The rate of resting heat production of 12 right ventricular rabbit papillary muscles was measured myothermically. Resting heat rate was measured at 4 temperatures (15, 20, 25 and 30 degrees C) in either 45% or 95% O2 while the muscle was passively stretched with various pre-loads. The metabolic substrate was pyruvate (10 mmol X 1(-1)). The mean resting heat rate, averaged across all treatment conditions, was 2.88 mW/g with no significant difference between the two oxygen concentrations. The calculated Q10 of the resting heat rate was surprisingly low--only about 1.4--but is shown to be in general agreement with literature values from whole heart oxygen consumption studies when the time-dependent decline is taken into account. Stretching the muscle beyond its rest length increased the rate of resting heat production. This response appeared unrelated to muscle diameter. The results are discussed in terms of the possible diffusion limitation of isolated papillary muscle preparations.