Gap junctional coupling and connexin immunoreactivity in rabbit retinal glia

Gap junctions provide a pathway for the direct intercellular exchange of ions and small signaling molecules. Gap junctional coupling between retinal astrocytes and between astrocytes and Müller cells, the principal glia of vertebrate retinas, has been previously demonstrated by the intercellular transfer of gap-junction permeant tracers. However, functional gap junctions have yet to be demonstrated between mammalian Müller cells. In the present study, when the gap-junction permeant tracers Neurobiotin and Lucifer yellow were injected into a Müller cell via a patch pipette, the tracers transferred to at least one additional cell in more than half of the cases examined. Simultaneous whole-cell recordings from pairs of Müller cells in the isolated rabbit retina revealed electrical coupling between closely neighboring cells, confirming the presence of functional gap junctions between rabbit Müller cells. The limited degree of this coupling suggests that Müller cell-Müller cell gap junctions may coordinate the functions of small ensembles of these glial cells. Immunohistochemistry and immunoblotting were used to identify the connexins in rabbit retinal glia. Connexin30 (Cx30) and connexin43 (Cx43) immunoreactivities were associated with astrocytes in the medullary ray region of the retinas of both pigmented and albino rabbits. Connexin43 was also found in Müller cells, but antibody recognition differed between astrocytic and Müller cell connexin43.