Temperature-dependent physiological stability of rat skeletal muscle in vitro

Stability of rat skeletal muscle contractile properties with time in vitro as a function of incubation temperature was characterized. Female Sprague-Dawley rats (8 wk, 148 g) were anesthetized with pentobarbital sodium (40 mg/kg, ip). Intact soleus (SOL) and extensor digitorum longus (EDL) muscles of 70- to 90-mg mass were removed and studied at incubation temperatures of 20, 25, 30, 35, and 40 degrees C. The average muscle thickness was 2.0 mm. Each muscle was studied at one temperature only. At 5, 15, 30, 45, and 60 min following immersion in an oxygenated Krebs-Ringer bicarbonate solution, isometric contractile properties were measured. Peak twitch tension, maximum tetanic tension, and rate of tension development of both SOL and EDL muscles were stable with time at 20 and 25 degrees C but decreased with time as a function of bath temperature above 25 degrees C. The calculated critical radius for O2 diffusion declined from 1.19 mm at 20 degrees C to 0.51 mm at 40 degrees C. For SOL and EDL muscles incubated at 25 degrees C, the histochemical demonstration of glycogen content was similar to that of fresh muscles, whereas muscles incubated at 40 degrees C showed staining for glycogen only in peripheral fibers. Observed and calculated results both infer a progressively larger hypoxic core at incubation temperatures above 25 degrees C.