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/

Inwardly rectifying potassium (K+) channels (Kir) in Muller cells, the dominant glial cells in the retina, are supposed to be responsible fo r the spatial buffering action of K+ ions. The molecular properties an d subcellular localization of Muller cell Kir channels in rat and rabb it retinas were examined by using electrophysiological, molecular biol ogical, and immunostaining techniques. Only a single population of Kir channel activity, the properties of which were identical to those of K-AB-2/KiP4.1 expressed in HEK293T cells, could be recorded from endfo ot to the distal portion of Muller cells. Consistently, Northern blot, in situ hybridization, and RT-PCR analyses indicated expression of Ki r4.1 in Muller cells per se. The Kir4.1 immunoreactivity was distribut ed in clusters throughout Muller cell membrane. The Kir4.1 expression in Muller cells disappeared promptly after culturing. When the dissoci ated Muller cells were cultured on laminin-coated dishes in the presen ce of insulin, Kir4.1 immunoreactivity was detected in a clustered man ner on the cell membrane. Because insulin and laminin exist in the sur rounding of Muller cells in the retina, these substances possibly may be physiological regulators of expression and distribution of Kir4.1 i n Muller cells in vivo.