Properties of retinal glial cell potassium channels

The patch-clamp technique was used to investigate the nature of potassium channels localised in the end-feet-membrane of Müller (glial) cells of the chicken retina. Two different preparations were used to examine ion channels in this membrane area. The ion channels were investigated either in eye-cup preparation, leaving the retina intact, or in isolated endfeet. In both preparations the ion channels showed identical characteristics. We found three K+ channels that could be distinguished by their electrical properties. In the inside-out configuration, in a standard bathing solution (6 mM potassium) with the pipette solution containing 100 mM potassium, these channels showed conductances of 15 pS, 29 pS and 68 pS. Whereas the 29 pS-channel was not voltage-dependent, the 15 pS- and 68 pS-channel showed significant voltage-dependence of the open-state probability. By membrane depolarisation the open-state probability of both channels types increased. The resting membrane potential of the glial cells was estimated to be about -80 mV, which is, as result of the high selectivity of the glial membranes for K+, more negative than that of retinal neurons.