Connexin50, a gap junction protein of macroglia in the mammalian retina and visual pathway

Reverse transcriptase-polymerase chain reaction (RT-PCR), Western blotting and immunocytochemistry were used to study the expression of gap junction proteins (connexins; Cx) in the rat and rabbit retina, RT-PCR of rabbit total retinal RNA using primers selected for the human Cx50 (α8 Cx) DNA template yielded cDNA fragments of the predicted base pair size. Western blots of rat and rabbit retinal membrane preparations probed with a monoclonal antibody which recognizes Cx50 in the lens of several mammalian species revealed a single band (MW 50 kD), identical to that recognized in lens membrane extracts. In frozen retinal sections of both species, the same monoclonal antibody as well as two polyclonal antisera raised against a synthetic peptide from the C-terminal region of the human Cx50 polypeptide labeled Muller cells and astrocytes. In Muller cells, labeling was strongest in the endfeet and in the filamentous processes ensheathing the photoreceptors. Extending from the neural retina, Cx50-like immuno- reactivity was detected in astrocytes of the optic nerve and along retinal projections within the CNS. Our data indicate that Muller cells and astrocytes of mammalian retinas and throughout the visual pathway are coupled through gap junctions composed of connexin50.