Membrane currents at large positive internal potentials in single myelinated nerve fibres ofrana pipiens

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  • LML. E. Moore
    L. E. Moore
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Abstract
A voltage clamp for single myelinated nerve fibers was developed from commercially available operational amplifiers. Under voltage clamp conditions steady-state currents were measured. The currents reached a maximum value at about E = +100 mV. Currents for greater potentials decreased. The preceding polarization markedly affected the magnitude of the delayed current at high cathodal potentials; however, the currents continued to reach maximum values. As predicted by the constant field theory, currents at high cathodal polarizations were essentially independent of the external K concentration. Also, these currents were independent of the external Ca concentration. Two pulse voltage clamp experiments showed that instantaneous outward currents did not reach a limiting value. The limiting steady-state current was reached with an exponential time constant of about 1 msec.

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