Müller cell function during spreading depression in frog retina.

K+ potentials were investigated using K+ microelectrodes in frog (Rana pipiens) retinas conditioned for spreading depression (SD) by Cl--free Ringer's solution. A marked increase in outside K+ concentration, [K+]O, maximal in the inner plexiform layer, was observed during SD. This [K+]o change resembled the simultaneously recorded membrane potential change in Müller cells, suggesting that these cells act as K+ electrodes. Intracellular recording with K+ electrodes in Müller cells showed that upon SD the [K+]i (inside) of Müller cells increases and therefore immediately starts to cleanse the extracellular space of the excess of K+ which, evidence suggests, is mainly caused by pathologically enhanced synaptic activity in the inner plexiform layer.