Patch-clamp experiments are well suited to investigate membrane transport processes on the molecular level. Such experiments can be performed on isolated cells, fragments of cells, and cells in tissue of different degrees of integration, under physiological or pathological conditions. We have used the chicken retina, which is a true piece of central grey matter without any blood-vessels to investigate the behaviour of ion channels, especially potassium channels, related to the retinal spreading depression (SD). The potassium channels of neurons mainly were of shorter lifetime and lower open state probability than those of glia (Muller) cells, and also conductances and selectivities were different. Both types of cells have voltage-sensitive as well as not voltage sensitive potassium channels. The properties of an excitation-depression wave in neuronal tissue (SD) can be explained at least partially on a molecular level by our results. In addition to the electrophysiological experiments, the whole-cell configuration of the patch-clamp technique has been used to fill cells with fluorescent dyes (especially Lucifer-Yellow), thereby identifying the cell under investigation.