Outwardly rectifying K+ channels display clustering in guinea pig retinal Müller cells

The cell-attached configuration of the patch-clamp technique was used to characterize the outward currents in acutely isolated Muller cells from the guinea pig retina. Sixty-five of 353 patches displayed macroscopic, outwardly rectifying currents due to depolarizing voltage steps. Single channel transitions were found in only two patches. The remaining patches did not reveal any voltage-dependent currents. Tail current analysis revealed a reversal potential close to the resting membrane potential. The currents disappeared if internal K+ was replaced by Cs+ in inside-out patches. From these results we conclude that guinea pig Muller cells possess voltage-dependent K+ channels that are distributed in clusters.