DIE MESSUNG UND BEDEUTUNG DER ELEKTRO‐LYTISCHEN POLARISATION IM NERVEN
Authors: LULLIES H. 
Published: January 2008

The importance of polarization in the behaviour of electrically stimulated nerves can only be elucidated by experiments in which the effects of both polarization and stimulus are measured at the same time.

With this in mind, both the resistance and the reactance of different nerves have been measured, sinusoidal alternating current covering a wide range of frequencies being used for stimulation. At the same time the dependence of current threshold on frequency has been investigated. Under certain conditions both the magnitude and the course of change of concentration (or of the change of charge) at the polarizable interfaces can be calculated from the resistance measurements. Supplementary measurements have been made with rectangular current impulses and condenser discharges.

The result, in the case of the sciatic nerve of the frog, is that the behaviour of the current threshold at low frequencies can only be explained intelligibly by the assumption of a certain process taking place in the tissue, which, like the “accommodation” of Nernst and of Hill, raises the electrical requirements at low frequencies, although there is no increased loss at the polarizable interfaces.

At frequencies about 200 cycles the effect of the stimulus is parallel to the quantity of electricity stored at the interface. However, the potential arising from this amount of electricity at the interface which is being studied is not at all constant at different frequencies.

If the potential at the interface be supposed to be the decisive factor (Nernst), which is in fact the more satisfactory assumption, then the interfaces whose polarization is mainly being measured cannot be those at which the important processes take place. Other interfaces must lie behind them, storing without loss at higher frequencies.

On the assumption that in non‐medullated nerves the important interfaces are exposed and more easily accessible for measurement, corresponding measurements were carried out on nerves of Maja, Octopus and Aplysia. Compared with the sciatic nerve of the frog, all resistances and threshold values are shifted towards the lower frequencies by 101·5 to 102·5. In fact, the effect of the current appears to correspond better with the calculated potential at the interfaces. This potential would be 3–8 mV. The available data, however, are insufficient for final conclusions.

The assumption of a process with a finite velocity, taking place in the tissue and caused by the electrical change, would give a satisfactory agreement between the potential theoretically deduced for constant potential at the interface and the experimentally established frequency relations to the current threshold at higher frequencies. In order to decide what is the influence of polarization on the behaviour of the current threshold at different frequencies, and what is to be attributed to processes taking place in the tissues, measurements under varied external conditions (length, temperature, electrolyte concentration, narcotics, poisons) will have to be carried out. Preliminary experiments show that both increase in the calcium content of the nerve and calcium decrease lead to a decrease in the total amount of polarization as compared with the normal. Calcium appears to act upon two different structures.

The frequency relation of the current threshold, on the other hand, is affected by calcium in one way only. The current threshold is always raised by an increase in calcium, more so at high than at low frequencies, the minimum of the frequency curve being shifted towards the lower frequencies.

Increase in potassium content leads to a decrease in polarization, the minimum of the current threshold being shifted towards the higher frequencies.

Up to the present these results merely support the conclusion that, on low frequency stimulation of the nerve, a process taking place in the tissue can be separated from the factors that govern the processes at higher frequencies. It is probable, however, that further investigations will enable us to state more accurately how and to what extent the effect of polarization and the influence of secondary processes in the tissue are expressed in terms of the time relations of the processes caused by electrical stimulation.