Membrane currents in human intercostal muscle at varied extracellular potassium

Abstract Hyperpolarizing and depolarizing square steps were imposed on the membrane potential of excised human intercostal muscle fibers by means of a 3‐microelectrode voltage clamp. The steady‐state amplitudes of the membrane currents inducing such steps were investigated as a function of the membrane potential, while the muscle was bathed in solutions varying in potassium content (K e = 1, 3.5, 7, 20, and 60 m M ). At all potassium concentrations, the membrane acted as a rectifier, both in the inward‐ and outward‐going directions. Inward currents were much reduced when K e was lowered from 3.5 to 1 m M , and were increased when K e was raised beyond 3.5 m M . The delayed outward current was reduced when K e was increased from 3.5 m M to 7 m M and higher potassium concentration. The results were qualitatively similar to those reported for rat skeletal muscle.