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Nange Jin, Friso Postma, Sean Youn, Eduardo Silveyra, David Paul, Stephen C Massey, Christophe P. Ribelayga; The Rod Connexin is Connexin36. Invest. Ophthalmol. Vis. Sci. 2016;57(12):583. doi: https://doi.org/.
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© ARVO (1962-2015); The Authors (2016-present)
Photoreceptors are electrically coupled via gap junctions. Rod/rod and cone/cone coupling are both present while rod/cone coupling provides an alternative pathway for rod signaling. In mammals, the gap junction expressed in cones has been identified as connexin36 (Cx36). However the identity of the rod connexin is unknown. To assess the role of Cx36, we compared wild type mice with a pan-Cx36 knockout and both rod and cone specific Cx36 knockouts.
The junctional conductance between pairs of adjacent rods was estimated using a perforated-patch clamp technique in the dark. The distribution of Cx36 in the outer plexiform layer (OPL) was assessed by confocal microscopy.
The junctional conductance between pairs of adjacent rods was ~ 150 pS in wild type mice (appropriate littermates) and close to 0 pS in pan-Cx36-/- or rod-Cx36-/- mice. In addition, the rod junctional conductance was ~ 75 pS in cone-Cx36-/- retinas. In the wild-type retina, most of the Cx36 in the OPL was found around the periphery of cone pedicles. A large fraction of this labeling was observed at points of contact between telodendritic processes and rod spherules. Cx36 labeling in the OPL was reduced by more than 90% in both the rod-Cx36-/- and the cone-Cx36-/- lines, except in small clusters underneath the cone pedicles where Cx36 is known to be associated with bipolar cell dendrites. In the rod-Cx36-/- line, a few remaining Cx36 plaques were found at contacts between cone telodendria.
Direct measurements of the rod junctional conductance demonstrate that Cx36 is required for rod electrical coupling. Intervening cones apparently account for ~ 50% of rod coupling. The distribution of Cx36 expression in the conditional lines indicates that rod-cone gap junctions require Cx36 on both sides (rod and cone) as the absence of Cx36 on either side prevents the formation of a plaque. This implies that 1) most of the Cx36 plaques observed in the OPL are rod-cone gap junctions. Thus, the rod/cone coupling provides an important pathway. 2) Cx36 is expressed in rods and required to form rod-cone gap junctions. 3) Altogether, the data strongly indicate that Cx36 is the rod connexin.
This is an abstract that was submitted for the 2016 ARVO Annual Meeting, held in Seattle, Wash., May 1-5, 2016.
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