Kinetics of the Negative After-Potential in Frog Single Nerve Fibers

¹ From the Department of Physiology, Washington University School of Medicine, St. Louis, Missouri

The time course of the negative after-potential from an isolated single nerve fiber is adequately described by the sum of two exponential terms. Conductance changes are confined to the relatively brief initial phase. The difference between active and resting membrane potential bears a relation to over-all membrane resistance which is consistent with the view that the first phase of the negative after-potential is dependent on a change in potassium conductance. The prolonged terminal phase of the after-potential is characterized by an exponential time constant identical with that of the slow drift in membrane potential (slow component of electrotonus) associated with the break of an anodal pulse. Both magnitude and time parameter of this terminal phase vary with pre-existent membrane potential. The differential changes in magnitude of spike and after-potential resulting from changes in pre-existent membrane potential suggest that the effects of anoxia on the after-potential/spike ratio are dependent only on the change in membrane potential.