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Sahar Farajnia, Maria de los Milagros Arietti, Maarten Kamermans; Circadian control of cone kinetics. Invest. Ophthalmol. Vis. Sci. 2017;58(8):4130.
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It is well known that cone responses are faster in the light-adapted than in the dark-adapted retina. A major part of this difference in kinetics comes from light/dark adaptational processes in the phototransduction cascade. In this study we investigated whether there is also a circadian control of cone kinetics.
Isolated goldfish retinas were prepared under dim red light for electrophysiological recordings during the day and night (12h-12h; LD) or subjective day and night (constant darkness; DD). Naturalistic stimuli were used to determine cone frequency response relations. Two-tailed Student’s t-test was applied for statistical analysis.
Voltage light responses of cones were faster during the day than during the night. This difference remained in DD conditions (n=17, p<0.001). To determine the underlying mechanism, we measured the cone frequency response relations under current and voltage clamp conditions. Responses under current clamp are shaped both by phototransduction and voltage gated currents whereas responses under voltage clamp are fully determined by the phototransduction cascade. Both current and voltage clamp recordings showed faster kinetics in the day than in the night (n=40; p<0.01). However, in DD conditions the change in kinetics was only present under current clamp conditions. This indicates that apart from light adaptation dependent change in the phototransduction, voltage gated channels control cone kinetics in a circadian fashion.We found that Ih, the current flowing through HCN channels, is the major current that is circadian-modulated in cone photoreceptor. Ih was larger in the day than in the night both in LD and DD (n=93; p<0.01). Previously we have shown that Ih changes the cone kinetics in a dynamic way, and induces temporal contrast adaptation (Howlett et al., submitted). Since Ih is circadian regulated, we tested whether contrast adaptation was circadian regulated as well. We found reduced contrast adaptation at night compared to the day both in LD and DD conditions (p<0.01).
These data show that Ih is under circadian control. During the day Ih is large making cones fast and allowing contrast adaptation. During the night Ih is attenuated, cones slow down and contrast adaptation is reduced. Circadian modulation of cone membrane properties seems to prepare the retina to transmit the appropriate visual signal depending on the time of the day.
This is an abstract that was submitted for the 2017 ARVO Annual Meeting, held in Baltimore, MD, May 7-11, 2017.
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