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One of the main functions of Muller glial cells is the performance of retinal K homeostasis which is thought to be primarily mediated by K fluxes through inwardly rectifying K (Kir) channels expressed in Muller cell membranes. Until now, there is limited knowledge about the types of Kir channel subunits expressed by Muller cells. Using RT-PCR, we investigated the expression of mRNA encoding different Kir channel subunits in the retina of the guinea pig. In order to verify expression by Muller cells, primary cultures of guinea pig Muller cells were also investigated. Both retinae and cultured Muller cells express mRNA for a diversity of Kir channel subtypes which include members of at least four channel subfamilies: Kir2.1, Kir2.2, Kir2.4, Kir3.1, Kir 3.2, Kir4.1, Kir6.1, and Kir6.2. mRNAs for the following Kir channel subtypes were not detected in Muller cells: Kir1.1, Kir2.3, Kir3.3, Kir3.4, Kir4.2, and Kir5.1. It is concluded that the spatial buffering of extracellular K by Muller cells may be mediated by cooperation of different subtypes of Kir channels, and that the distinct Kir channel types involved in this function may change depending on the physiological or metabolic state of the retina.

(C) 2002 Lippincott Williams & Wilkins, Inc.