Abstract
Purpose :
In mouse retina, rods and cones are electrically coupled by gap junctions made of connexin36 (Cx36). Rod/cone coupling allows light-evoked signals that originate in rods to enter cones and alter the cone membrane potential in a way that directly reflects the low threshold and slow kinetics of the rod light responses. Rod/cone coupling is not static however and is modulated by light/dark and/or circadian factors along a wide dynamic range. It remains unclear how fast these changes are implemented. We used the amount of rod signal in the cone photovoltage as a proxy to study the kinetics of rod/cone coupling increase or decrease during light/dark adaptation and/or pharmacological treatments.
Methods :
Experiments were conducted on dark-adapted perfused retinal sections from wild type (WT) mice (C57BL6/J) or from mice lacking rod/cone coupling (Cx36-KO mice) (Jin et al. 2020 Science Adv. 28, aba7232). Patch-clamp recording of single cone pedicles was performed in response to series of 20-ms light flashes of increasing intensity. Light adaptation was obtained by presenting a full-field light stimulus against a dark background (500 ms in duration, 0.5 Hz) that was turned off immediately before running the intensity series every 5 min. We used the threshold of the cone photovoltage as well as the area of the slow component present at higher intensities to quantify the rod-originated signal contribution to the cone photovoltage. A reduction or increase in the rod contribution was interpreted as a decrease or an increase in rod/cone coupling, respectively.
Results :
Bright light adaptation (2,000 R*/rod/500-ms, 0.5 Hz) of dark-adapted WT cones eliminated the rod component in the cone photovoltage within 10-15 min (n=5). The threshold and shape of the photovoltage of dark-adapted Cx36-KO cones were identical to those of light-adapted WT cones after 15 min (n=5). Application of the gap-junction blocker meclofenamic acid (MFA) eliminated the rod input to dark-adapted WT cones within 15 to 30 min (n=6) but had no effect on the photovoltage of dark-adapted Cx36-KO cones (n=6).
Conclusions :
The data reveal the relatively slow kinetics of rod/cone decoupling that take tens of minutes to fully develop. Experiments are underway to determine the kinetics of the dark- and/or pharmacologically induced increase in rod/cone coupling.
This abstract was presented at the 2024 ARVO Annual Meeting, held in Seattle, WA, May 5-9, 2024.