Distribution of connexin43 immunoreactivity in the retinas of different vertebrates

The distribution of Connexin43 (Cx43) was examined by immunoblotting and immunofluorescence microscopy in the retinas of five different vertebrates by using a C-terminal specific peptide antibody. The specificity of the antibody was proved on immunoblots, in which it showed cross reactivity with a 43-kDa protein in rat heart homogenates as well as in homogenates of rabbit, rat, chicken, turtle, and fish (carp and zebrafish) retinas. Immunofluorescence histochemistry with retinal cryosections revealed the presence of Cx43 in the retinal pigment epithelium cells of all tested species and in blood vessels of vascularized retinas (fish and rat). Cx43 immunoreactivity was further localized in the stria medullaris of rabbit retina, in the nerve fiber layer of rat retina, most likely in astrocytes, and in the area of the outer limiting membrane of the fish retina, most likely representing Cx43 in Müller glia cells. A punctate Cx43-immunoreactive pattern consistent with gap junctions was also detected in the outer plexiform layer of carp and zebrafish retinas, and a specific amacrine cell type, which ramified in two layers of the inner plexiform layer, was labeled in the zebrafish retina. The present results are in accordance with previous findings showing the abundance of Cx43 in astrocytes, endothelium, and epithelial cells. However, the presence of Cx43 immunoreactivity in a specific population of amacrine cells of the zebrafish retina might indicate that a Cx43-like protein is also expressed in neurons.