The effect of the CO2/HCO3- buffer system on the membrane potential of frog skeletal muscle.

1. The membrane potential of frog skeletal muscle was measured in various solutions, in the presence and in the absence of the CO2/HCO3- buffer. 2. The CO2/HCO3- buffer (PCO2 = 38-593 mm Hg; [HCO3-] = 5-25 mM/1) generally induced a reversible depolarization. 3. In the presence of C1-, there was a slowly developing but marked depolarization. 4. In the absence of C1-, there was an early depolarization which increased in high-PCO2 or low-K+ solutions, and decreased in low-PCO2, high-K+ or Na+-free solutions. Changing the HCO3- concentration did not modify the depolarization. 5. The early depolarization and contractions observed in C1--free Ringer persisted in presence of tubocurarine chloride (2.5-10(-5) M/1). 6. Possible mechanisms for the depolarization are discussed.