Oscillation of the electric potential of frog skin under the effect of Li+: Experimental approach

Abstract

When a frog skin is used to separate two compartments, and lithium is added to the external medium, transmembrane electric potential oscillations frequently occur. When no external current is imposed, sustained oscillations, with a period of about 10 min, are maintained for several hours. An oscillation of the Na+ influx accompanies the electric oscillation, though the two oscillations are out of phase to a greater or less extent. Theophyllin promotes a significant decrease in the mean electric potential of the skin, but it does not affect very much the characteristics of the oscillation. Important factors influencing the oscillation are temperature, permeability of the external membrane to lithium, and potassium concentration in the internal medium. No correlation can be detected between oscillation characteristics and skin area. This suggests that the oscillation is of a local nature, possibly originating at the cellular level. Occurrence of macroscopic oscillations implies coupling between local oscillators. Coupling between two epithelia has been studied under diverse conditions. The coupling is of an electrical nature: by varying the value of the coupling resistance, it is possible to control synchronization of the oscillations.

Quasi-periodic behaviour in a model for the lithium-induced, electrical oscillations of frog skin

“…The shape of the oscillation curve suggests the occurrence of an interference between several individual oscillatory processes. Adapted from [9]. skin under study [9].…”

“…Adapted from [9]. skin under study [9]. In another series of experiments, using subcompartmentalised chambers, it has been possible to study simultaneously different parts of a single skin subjected to identical ionic conditions [9].…”

“…skin under study [9]. In another series of experiments, using subcompartmentalised chambers, it has been possible to study simultaneously different parts of a single skin subjected to identical ionic conditions [9]. It turned out that the different parts of the skin exhibited oscillations of their electric potential difference, but these oscillations were out of phase with each other; moreover, the amplitude of these oscillations and the time during which each of them was sustained varied from one zone of the skin to another.…”

“…Our group [7,9] has shown experimentally that (i) when no transepithelial potential is imposed, sustained oscillations with a period of about 10 min are maintained for several hours, (ii) an oscillation of the Na + influx accompanies the electric oscillation (the two oscillations have approximately the same period but are not in phase), (iii) under conditions of imposed potential the transepithelial electric current has damped oscillations, (iv) the shape of the oscillations in potential is quite variable (from almost sinusoidal to very complex), (v) theophyllin (which induces an accumulation of cyclic AMP within the cells) promotes a significant decrease in the mean electric potential of the skin, but does not affect the characteristics of the oscillation very much, (vi) the osmotic pressure has little effect on the oscillation and (vii) important factors influencing the oscillations include temperature, the permeability of the external membrane to lithium and the potassium concentration in the internal medium.…”

“…1). Our group has been particularly involved in the under-standing of the generation of such oscillations, from both experimental and theoretical points of view [7][8][9][10][11]. As it will be explained in section 3, a set of two ordinary differential equations were obtained to describe the dynamics of a fragment of the skin.…”