Ion Channels of the Retinal Pigment Epithelium

Abstract

Ion channels contribute to or permit almost every cell function. This importance is highlighted by the definition of the so-called channelopathies as a disease term. These channelopathies are caused by changes of ion channels itself either by mutation of ion channel genes or by changes in the control of ion channel activities. The RPE is a close interaction partner of the photoreceptors and changes of this interaction leads to retinal degeneration. For almost all RPE functions also ion channels are involved so that the analysis of RPE’s ion channels and their contribution to the RPE function does not only help to understand the interaction of the RPE and the photoreceptors but also the mechanisms of disease. This chapter describes the profile of ion channels that are known in the RPE, their contribution to RPE function and their role in retinal degeneration. The profile includes Cl channels such as anoctamin-2, bestrophin-1, CCl-2 or CFTR, K+ channels such as Kir7.1 or KCNQ4/5 and Ca2+ channels such as Cav1.3, TRPC or TRPV2. In particular, the analysis of Cl channels provided basic information on mechanisms of transepithelial transport of Cl- and water across the RPE. Furthermore, the analysis of K+ channels shed light onto spatial K+ buffering that maintains the excitability of photoreceptors. Finally, the analysis of ion channels that contribute to intracellular Ca2+ homeostasis helped to decipher new regulatory mechanisms for secretion of growth-factors, phagocytosis of shed photoreceptor outer segments and transepithelial transport.