Na,K-ATPases of the Human Retina and Optic Nerve

Abstract

Abstract: : Purpose: . Retinopathy and macular edema are common ocular complications of diabetes that lead to vision impairment or blindness. Both complications have common properties, the most obvious being changes in barrier function and fluid regulation. Critical to the maintenance of cell volume as well as intracellular and extracellular monovalent cation levels are the Na,K-ATPases which use the chemical energy of ATP hydrolysis for the vectoral uphill exchange of 3Na+ for 2K+ across the plasma membrane. Fluid flow is indirectly dependent upon the Na,K-ATPases because of the differences in the hydration spheres of the two cations. Therefore, to commence our study of the barrier function and fluid flow of the retina, the location of the three Na,K-ATPase catalytic subunit isoforms (ATP1A1, ATP1A2, ATP1A3) was determined using indirect immunofluorescence microscopy. Methods: Sections of fixed posterior poles of human eyes were treated with affinity purified polyclonal rabbit antibodies to the three catalytic subunit isoforms, monoclonal antibodies to marker proteins (GFAP for glia, vimentin for Muller cells, calbinden for amacrine and horizontal cells, parvalbumin for horizontal cells, smooth muscle action for vascular smooth muscle, and ZO1 and occluding for tight junctions) followed by Alexa-594 GAM and Alexa-488-GAR secondary antibodies, then counterstained with DAPI. Results: For nondiabetic subjects, ATP1A1 was located in selected cone inner segments, selected Muller cell end-feet, both plexiform layers, selected cell bodies of the INL and ganglion cell layers and the vascular endothelium. ATP1A2 was located in a majority of the Muller cell end-feet, glia of the retina, optic nerve head and optic nerve, selected cone inner segments and selected cell bodies of the INL. ATPIA3 was located in the optic nerve, the rod inner segments, selected cone inner segments, vascular smooth muscle and selected cell bodies of the ONL, INL and GCL. The major differences in the diabetic retina were a loss of all isoforms in the cell bodies of the ONL, INL, and GCL and a marked decrease in ATP1A2 in the retina and optic nerve glia. Conclusions: The marked decrease in the ATP1A2 isoform in GFAP-positive cells may contribute to the loss in barrier function in the neural retina and optic nerve.

Keywords: NaK ATPase • retinal glia • diabetes