Extracellular potassium alters frequency and profile of retinal spreading depression waves

The phenomenon of spreading depression (SD) was observed in chicken retina by means of optical registration via a microscope and a CCD camera applying modern methods of image processing for optimized evaluation of the wave profiles. The propagation dynamics of SD waves was investigated as a function of extracellular potassium. Two main findings were obtained. Firstly, the frequency of spontaneous wave generation increased with the increase of K+ concentration. Secondly, there was an effect of potassium on the wave profile. In particular, the recovery zone of SD waves was shortened at increased K+. This effect was not only due to the dispersion relation of waves in excitable media as shown by the result of the mechanically induced wave trains. Applying the basic principles of chemical excitability for the interpretation of the data led us to the conclusion that these potassium effects are due to perturbations of an autocatalytic reaction to be further explored.