The asymmetric, rectifier-like I-V curve of the Na/K pump transient currents in frog skeletal muscle fibers

The Na/K pump transient currents in skeletal muscle fiber were identified using an improved double Vaseline gap voltage clamp technique. The asymmetric characteristics of the pump current-voltage relationship were studied. The definition of the Na/K pump currents was the ouabain-sensitive currents, where ouabain is a specific Na/K ATPase inhibitor. Membrane potential was held at -90 mV, the membrane resting potential. A series of stimulation pulse-pairs symmetric to the membrane resting potential were applied to the cell membrane. The summation of the currents responding to the two pulses in each pair indicates the asymmetry of the pump currents with respect to the membrane resting potential. The voltage dependence of the Na/K pump transient currents from skeletal muscle is similar to the steady-state I-V curve from either skeletal muscle fibers or cardiac muscles. It is a sigmoidal-shaped, asymmetric curve with respect to the membrane resting potential. This asymmetric, rectifier-like voltage dependence indicates that a symmetric oscillating membrane potential may generate a net, outward pump current. In other words, the Na/K pump molecules may be activated by an oscillating membrane potential. (C) 2002 Published by Elsevier Science B.V.