Oxygen cost of twitch and tetanic isometric contractions of rat skeletal muscle.

The distal muscles of a rat single hindlimb preparation, perfused at 14-15 ml/min, were stimulated sequentially for 10-min intervals at 12, 24, 36, 48, 60, 75, and 120 twitch/min (8 V, 0.05 ms) or at 7.5, 15, 30, 45, 60, 75, and 90 tetani/min (100-ms train, 100 Hz). Oxygen consumption (VO2) of the whole muscle increased up to 6- and 10-fold over rest during twitch and tetanic conditions, respectively. Tension development during each stimulation interval decreased sequentially at the higher contraction frequencies. VO2, corrected for this loss in tension development, increased linearly with contraction frequency with a slope of 0.037 +/- 0.003 mumol O2 X g-1 X twitch contraction-1 and 0.260 +/- 0.034 mumol O2 X g-1 X tetanic contraction-1. This sevenfold difference in slopes, which represent the O2 cost of a single contraction without fatigue, corresponds to the difference in developed tension between twitch and tetanic contractions. Anaerobic metabolism was negligible during tetanic contractions, but was significant during some twitch conditions. These values probably represent the O2 cost for fast-twitch muscle, since this is the predominant type (greater than 90%) in the rat hindlimb. However, an approximate fourfold difference in blood flow (determined with microspheres) between the white and red gastrocnemius sections (predominantly fast-twitch white and fast-twitch red, respectively) suggested a disparity in metabolic response. Estimates of the peak VO2 for each fiber type, for our perfusion conditions, are 6- and 30-fold above rest, respectively.(ABSTRACT TRUNCATED AT 250 WORDS)