Minimizing the influence of the series resistance in potential clamped Ranvier nodes.

Series resistance artifacts in ionic current measurements on single myelinated nerve fibres are commonly minimized by reducing sodium currents. Doing this some deviations from the predictions of the Hodgkin-Huxley-Frankenhaeuser formalism become evident. In the present investigation two methods to reduce sodium currents were used with and without compensated feedback to examine the influence of the nodal series resistance. Changing the availability of sodium permeability by appropriate prepulses peak sodium current-voltage relations obeyed the Hodgkin-Huxley-Frankenhaeuser formalism only provided the amount of compensated feedback was set to give minimum of the current-voltage relation near E = 0. For reduced sodium concentration in the bathing fluid the so-called independence principle predicts a shift of the minimum of the current-voltage relation on the potential axis in negative direction as compared to ordinary Ringer solution, if the effective series resistance is sufficiently small. This was confirmed by experiments only if the above mentioned amount of compensated feedback was used. The results suggest that the "E = 0"-criterion indicates optimum compensation of the influence of the series resistance.