Novel roles for voltage sensitive ion channels in retinal pigment epithelium and phagocytosis

Summary Photoreceptors of the retina undergo a daily renewal process where they shed 10% of their outer segment disks that are then digested by the retinal pigment epithelium (RPE). Recent work demonstrated that L‐type calcium channels in RPE are important for the diurnal regulation of this process. We investigated the regulatory role of several ion channels of the RPE in phagocytosis using human embryonic stem cell (hESC)‐derived RPE and freshly isolated mouse tissue. The ion channels were first characterized by patch clamp recordings. The localization of photoreceptor outer segments (POS) and different ion channels during phagocytosis were studied by incubating hESC‐derived RPE with purified POS particles or by dissecting mouse RPE during the physiological peak of POS shedding. Our phagocytosis assays and subsequent immunolabeling showed a promising co‐localization between certain voltage sensitive ion channels, opsin and proteins involved in the phagocytosis pathway. Moreover, blocking the activity of these channels significantly reduced the efficiency of the process. Overall, several types of ion channels appear to be involved in the phagocytosis pathway. Yet, more work is required to assess their specific role.