Purchase this article with an account.
Rachel Fischer, Roman Lazarenko, Qi Zhang, Rebecca M Sappington; Altered potassium homeostasis in glaucoma and significance for retinal ganglion cell health. Invest. Ophthalmol. Vis. Sci. 2017;58(8):2018.
Download citation file:
© ARVO (1962-2015); The Authors (2016-present)
Degeneration of retinal ganglion cells (RGCs) in glaucoma is spatially heterogeneous. We tested the hypothesis that heterogeneous degeneration is reflected in RGC physiology and related cation homeostasis.
Intraocular pressure (IOP) was elevated bilaterally in C57Bl/6 mice, using the microbead occlusion model. Control mice received equivalent, bilateral injections of saline. After 4 weeks IOP elevation, the neural tracer cholera toxin beta (CTB) was injected intra-vitreally to assess the degenerative state of RGCs. Single-cell, current clamp recordings were performed on CTB+ RGCs and the amplitude and frequency of spikes at +20pA current steps was correlated with degree of CTB uptake. To examine cation homeostasis, we assessed cation channel expression and localization in retina from microbead- and saline-injected eyes, using western blot and immunohistochemistry, respectively. To examine pressure-induced changes in cation flux specifically in RGCs and Müller glia, we exposed primary, purified cultures to elevated hydrostatic pressure for 48 hours and measured both the concentration of cations in culture media (inductively-coupled plasma mass spectrometry) and cation flux (Thallium flux imaging).
Retina from microbead eyes exhibited heterogeneous uptake of CTB by RGCs, where areas of high to low CTB labeling were detected within a single retina. RGCs with low CTB uptake exhibited decreased ability to maintain the frequency and amplitude of spikes with increasing current applied. The current threshold for deficits in spike frequency and amplitude positively correlated with CTB intensity. Immunolabeling intensity for both TASK-1 and TREK-2 K+ channels substantially decreased in Müller glia and RGCs from microbead retinas, as compared to controls. In primary cultures of purified RGCs and Müller glia exposed to elevated pressure, the extracellular K+ concentration increased by 75% and 12% (p=0.001), respectively. Correspondingly, cation conductance diminished by 8% (p=0.03) and 5% (p=0.007) in Müller glia and RGCs, respectively.
These data indicate the potential for disruption of K+ homeostasis in glaucomatous retina that is likely mediated by altered cation conductance in Müller glia and RGCs. Localized changes in cation homeostasis could underlie electrophysiological impairment in RGCs with the potential to propagate this dysfunction to neighboring RGCs.
This is an abstract that was submitted for the 2017 ARVO Annual Meeting, held in Baltimore, MD, May 7-11, 2017.
This PDF is available to Subscribers Only