Effects of bicarbonate on resting potentials in mammalian skeletal muscle

In the absence of external HCO 3 , resting membrane potentials (Vm) in extensor digitorum longus muscle were depolarized as compared to the normal Vm in the presence of HCO 3 . Removal of Na or Cl from the HCO 3 ‐free media induced repolarization. In muscle in HCO 3 buffer at 20°C, internal K, Na, and Cl activities were analyzed with liquid ion selective microelectrodes. The averages were respectively, 119.7 ± 2.1, 6.69 ± 0.3, and 3.41 ± 0.06 mM. In a high proportion of cells analyzed, the equilibrium potential for Cl was negative to Vm. Removing external HCO 3 , decreased internal K while internal Na and Cl increased. An increase in temperature and the application of HCO 3 significantly lowered internal activities of both Na and Cl. Removal of HCO 3 with temperature held constant caused a rapid depolarization, an increase in internal Na and Cl, and a decrease in internal K. Furosemide (10 μM) induced a repolarization of cells that were previously depolarized in the HCO 3 ‐free state, but the drug does not decrease internal Na.