The increase in the rate of heat production of frog's skeletal muscle caused by hypertonic solutions.

1. The rate of heat production of resting muscle is increased by hypertonic solutions.2. The threshold osmolality required to produce the increased heat rate is less than 2 times normal; at 2.5-3 times normal the heat production rises to 20-50 mcal.g(-1).min(-1), which is 10-20 times the basal rate.3. In anaerobic conditions, the effect of hypertonic solutions on heat rate is only one tenth of that in aerobic conditions.4. A glycerol-treated muscle, with damaged tubular system, still gives a normal response to hypertonic solutions, though it does not respond to raised K(+) concentration.5. The metabolic response to hypertonic solutions is considerably suppressed by procaine.6. Ouabain, 10(-5)-10(-4)M, has no effect.7. The response remains substantial in a muscle which has been depolarized in isotonic K(2)SO(4).8. The membrane potential is slightly reduced by hypertonic solutions, but this cannot account for the increase of the resting metabolism.9. It is suggested that the effect may be due to the release of calcium ions, which produce an increase in myosin ATPase activity.