The effect of bicarbonate concentration on fatigue and recovery in isolated rat diaphragm muscle

Abstract

Diaphragm strips from young rats (45–60 g) about 0.3 mm thick were fatigued by tetanic stimulation at a train repetition rate of 2 Hz for 3 min. The isometric tension developed was measured during fatigue and recovery in solutions containing 25, 10, or 2 mM bicarbonate at both 37 and 30 °C. Tension fell during fatigue to between 20 and 30% of the initial value and this was not significantly influenced by external bicarbonate concentration or temperature over the range considered. Recovery of tension was complete and rapid (t1/2 < 1 min) in 25 mM bicarbonate at both temperatures. In 10 and 2 mM bicarbonate recovery was slowed (t1/2 3.5 and 7 min, respectively, at 30 °C, 1.6 and 4.5 min at 37 °C) and incomplete (85 and 72% at 30 °C, 82 and 61% at 37 °C).Muscle creatine phosphate fell during fatigue but was completely restored within 4 min at 30 °C in either 2 or 25 mM HCO3. Lactate increased less in muscles fatigued in 2 mM HCO3 and fell at a slower rate during recovery. The results seem to exclude intracellular creatine phosphate concentration as a major determinant in recovery. The evidence suggests that external bicarbonate can affect the recovery of tension following fatigue by altering intracellular acid-base balance.