The Conditions for Initiating "All-or-Nothing" Repolarization in Cardiac Muscle.

Solutions have been computed for the point polarization of an infinite cable-like membrane obeying the equations used to reproduce the Purkinje fiber action potential (Noble, 1960, 1962a) in order to determine the conditions for initiating all-or-nothing repolarization during the action potential plateau. It was found that all-or-nothing repolarization would not be obtainable during the first half of the action potential in spite of the fact that the membrane current-voltage relations contain regions of negative conductance. At the point at which the all-or-nothing response is first obtained, the computed threshold is large and repolarization almost back to the resting potential would be required in order to initiate the response. The results are discussed in relation to the experimental evidence at present available on repolarization in heart muscle.