Martin Diep, Michele C Madigan,Krisztina Valter-Kocsi, Barbara Junghans

Purpose:
Aquaporin-4 (AQP4) and potassiumchannel Kir4.1 are normally expressed by retinalMüller glia, and play a major role in controlling retinalfluid movement and maintaining retinal integrity andfunction. We investigated AQP4 and Kir4.1 distribu-tion and expression in adult post-mortem human eyesand eyes with long-term serous retinal detachmentsecondary to choroidal melanoma.

Methods:
Paraffin sections of fixed central (maculaand optic disc) and peripheral choroid/retina fromyoung (70 years, n = 4)human post-mortem eyes, and whole human eyesremoved for choroidal melanoma (n = 5), wereco-immunolabelled with antibodies to AQP4, Kir4.1and GFAP. Localisation and distribution of immuno-labelling was assessed using immunofluoresence andconfocal microscopy.

Results:
Regions of detached retina were thinned,with a reduced ONL and OPL. Disorganised retina wasseen overlying the anterior melanoma surface associ-ated with extensive Müller cell gliosis. Increased GFAPexpression consistent with Müller cell reactivity wasalso observed associated with serous retinal detach-ment. Immunolabelling showed differential expressionof AQP4 and Kir4.1 in detached retinas, withupregulation of AQP4 and downregulation of Kir4.1compared to unaffected eyes. This was most obvious inretina overlying melanomas, and in retina separatedby serous exudate from underlying retinal pigmented epithelium.

Conclusions:
Decreased expression of Kir4.1 hasbeen suggested (in animal models) to be associatedwith Müller cell proliferative gliosis in response toserous retinal detachment. Increased AQP4 expressionobserved in areas of retinal detachment may occurrelated to altered retinal fluid balance secondary tophotoreceptor degeneration and compromise of theouter blood-retinal barrier.