Effects of deuterium oxide on mechanics and energetics of skeletal muscle contraction.

Mechanics and energetics of contraction were studied in isolated frog semitendinosus muscles (n = 15) in deuterium oxide (D2O) at 5 degrees C. Twitch force and energy liberation (heat + work) in 99.8% D2O-Ringer at lo were 4 +/- 0.8 and 22 +/- 1%, respectively, of control values. Tetanus force was slowed in development, and developed tetanus force was reduced to 89 +/- 7% of control values. With repeated tetanic contractions, the rate of force development increased, and peak force increased above control values in some muscles. The twitch was potentiated 10-fold (10 +/- 2) after repeated tetanic contractions. Energy liberation increased but not in proportion to force. Ca2+ cycling energy liberation or activation heat, estimated from stretched muscles, was 60 +/- 3% of control values. With maximum posttetanic twitch potentiation, the activation heat increased by 25 +/- 3%. Peak twitch force and energy liberation occurred at longer muscle lengths than in normal Ringer. After correcting for small differences in force development at lo and 1.38 +/- 0.01 lo, it was possible to estimate the effect of length per se on energy liberation. Under these conditions, there was an 8 +/- 2% decrease in energy liberation at 1.38 lo.