NEGATIVE AFTER-POTENTIAL OF FROG'S SKELETAL MUSCLE

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Abstract
When investigated with inside-the-cell micro-electrodes, a linear relation was found between the amplitude of the negative after-potential and the resting potential. This relation was not altered by changing the external Na+ concentration, increasing the external K+ concentration or moderate veratrine treatment. It was upset by great reduction of the external K+ concentration or prolonged soaking in Ringer''s or low K+ solutions. The decline of the negative after-potential was found to be exponential and its time constant ([tau]m) was similar to that for the decline of an impressed hyperpolarization. Results support the view that the rapid repolarization phase of the action potential ends with the membrane slightly depolarized and the negative after-potential is a passive return of the membrane potential back to resting levels. There was also evidence indicating a slight increase in the Na conductivity over resting levels. The increased inward movement of Na+ which results from this condition slightly slows down the repolarization.

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