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Christophe Ribelayga, Nange Jin, Zhijing Zhang, David Paul, Stephen C Massey; Electrical Coupling between Mouse Rods: Direct Measurements of the Junctional Conductance Uncover the Identity of the Rod Connexin and Demonstrate Circadian Control of Rod Electrical Coupling . Invest. Ophthalmol. Vis. Sci. 2015;56(7 ):1714.
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© ARVO (1962-2015); The Authors (2016-present)
Evidence from EM studies and electrical recordings from single rods suggest that rod photoreceptors are electrically coupled by gap junctions in mouse retina. A circadian clock controls the state of rod electrical coupling so that rod coupling is weak during the day and stronger at night. Yet, the rod connexin remains to be identified and direct measurements of junctional conductances between pairs of adjacent rods are missing. Here we performed paired recordings of adjacent rods 1) in C57Bl/6J mice that lack the gap junction forming connexin36 (Cx36), and 2) in melatonin-proficient CBA/CaJ mice at different times in the circadian cycle.
Perforated patch-clamp recordings from pairs of adjacent rod photoreceptor somas were performed simultaneously under dark-adapted conditions in mouse retinal slices maintained by superfusion at 32°C. The voltage of one rod was held constant (Vh = -35 mV) and changes in membrane current were measured in response to voltage steps (50 ms, 10 mV increments from -50 to +50 mV) applied to the other rod. The junctional conductance was estimated for each pair from the slope of the transjunctional current - transjunctional voltage relationship.
The rod-rod junctional conductance ranged from 117 to 495 pS in the Cx36+/+ wild type mice with an average of 301 ± 109 pS (n = 3) but was below the resolvable limit given measurement noise in Cx36-/- littermates (n = 2). In CBA/CaJ retinas, we found estimates of the rod-rod junctional conductance ranging from 0 to 699 pS with an average of 274 ± 113 pS during subjective day (n = 6). During subjective night, estimates were higher, ranging from 471 to 2,255 pS with an average of 1,062 ± 413 pS (n = 4).
Our data indicate that Cx36 is required for electrical coupling between mouse rods. In addition, our data provide direct evidence that the rod junctional conductance increases at night in CBA/CaJ mouse retina, further supporting the view that rod electrical coupling is controlled by a circadian clock.
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