Differential susceptibility of rat retinal neurons to the Na+/K+-ATPase inhibitor ouabain.

Na+/K+-ATPase (NKA) is an important transporter responsible for maintaining intracellular ion homeostasis. To identify retinal cell types most susceptible to NKA inhibition, we examined the effects of ouabain, an NKA inhibitor, on different retinal cell types in rats. Male Sprague-Dawley rats were used for this study. The effects of ouabain on the retina were assessed at 2, 7, and 14 days after intravitreal injection, using retinal histology, immunolabeling with cell-specific markers, and electroretinogram recordings. We observed a decrease in the number of cells in the ganglion cell layer (GCL) and inner nuclear layer (INL) after ouabain injection. Specifically, the number of NeuN- and Brn3a-positive cells in the GCL, as well as NeuN-, parvalbumin-, calretinin-, and choline acetyltransferase-, and secretagogin-positive cells in the INL, were significantly reduced in ouabain-injected eyes. The reduction in cell numbers in the INL occurred in the following order of susceptibility: parvalbumin-positive cells were most affected, followed by calretinin-positive cells, and then secretagogin-positive cells, and finally choline acetyltransferase- or NeuN-positive cells. Protein kinase Cα- and Sox9-positive cells showed modest changes, but calbindin-D-28k-positive cells remained unchanged. NKA α1 subunit was broadly expressed in the rat retina, whereas the ouabain-sensitive NKA α2 and/or α3 subunits were present in all retinal neuronal cells and in Müller cells. The electroretinogram showed significant reductions in both a- and b-wave amplitudes. These findings suggest that amacrine cells are particularly susceptible to NKA inhibition compared to other retinal cell types, and this differential susceptibility may contribute to cell type-specific damage in retinal neurodegenerative diseases.