Abstract
Purpose :
We are testing the hypothesis that retinal ganglion cell (RGC) dysfunction in response to oxidative species can be detected electrophysiologically and that it differs between RGC subtypes. Compromised mitochondrial ATP synthesis increases levels of reactive oxygen species (ROS), causing oxidative damage to cells, impairing protein function, and may lead to cell degeneration. Our data suggest that during metabolic crisis there could be alterations to the responses of RGCs to visual stimuli, with concomitant changes to the overall retinal output to the brain.
Methods :
Current-clamp recordings of identified α RGCs in flat-mount preparations were made from wildtype, OPN4-GFP and KCNG-cre-tdTomato mouse retinas. Light stimulation was used to define the subtype of RGC and to assess RGC modulation. RGCs were superfused with mercaptosuccinate (MCS, which blocks glutathione peroxidase and increases oxidizing species). Additional agents, some applied via the patch electrode, include, H2O2, catalase and antimycin A.
Results :
ON sustained RGCs produced 19.3 ± 4.0 spikes at a peak rate of 59.9 ± 5.4 Hz in response to a 1 second light stimulus under control conditions, and responded to MCS superfusion with a reduced number of spikes in response to light, 11.2 ± 3.6, at a peak rate of 28.4 ± 5.1 Hz (p<0.0005). ON transient RGCs under control conditions produced 4.7 ± 0.9 spikes in response to a 1 second light stimulus at a peak rate of 37.9 ± 5.4 Hz. In the presence of 1 mM MCS they produced 9.5 ± 1.6 spikes in response to light at a peak rate of 52.7 ± 8.1 Hz (p<0.05). Recordings from labeled OFF transient and sustained α cells, and unlabeled ON-OFF transient and sustained RGCs, also followed this trend suggesting that excitability of transient cells increases in response to elevated ROS.
Conclusions :
These results show that RGC excitability is strongly altered by reactive oxidative species. Increased levels of oxidants increased transient RGC spiking and reduced sustained RGC spike rates. Further investigations aim to provide an explanation for the opposing actions of oxidant stress on transient and sustained RGCs. Examination of changes to voltage-gated Na and K channels, other ion channels, as well as excitatory and inhibitory synaptic inputs, that may underlie the oxidative modulation of excitability, are warranted.
This is a 2020 ARVO Annual Meeting abstract.