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.