Expression and clustered distribution of an inwardly rectifying potassium channel, K(AB)-2/Kir4.1, on mammalian retinal Muller cell membrane: Their regulation by insulin and laminin signals

Abstract

Inwardly rectifying potassium (K+) channels (Kir) in Muller cells, the dominant glial cells in the retina, are supposed to be responsible for the spatial buffering action of K+ ions. The molecular properties and subcellular localization of Muller cell Kir channels in rat and rabbit retinas were examined by using electrophysiological, molecular biological, and immunostaining techniques. Only a single population of Kir channel activity, the properties of which were identical to those of K(AB)-2/Kir4.1 expressed in HEK293T cells, could be recorded from endfoot to the distal portion of Muller cells. Consistently, Northern blot, in situ hybridization, and RT-PCR analyses indicated expression of Kir4.1 in Muller cells per se. The Kir4.1 immunoreactivity was distributed in clusters throughout Muller cell membrane. The Kit4.1 expression in Muller cells disappeared promptly after culturing. When the dissociated Muller cells were cultured on laminin- coated dishes in the presence of insulin, Kir4.1 immunoreactivity was detected in a clustered manner on the cell membrane. Because insulin and laminin exist in the surrounding of Muller cells in the retina, these substances possibly may be physiological regulators of expression and distribution of Kir4.1 in Muller cells in vivo.