Physiological and Molecular Characterization of Connexin Hemichannels in Zebrafish Retinal Horizontal Cells
- Authors
- Sun, Z., Risner, M.L., van Asselt, J.B., Zhang, D.Q., Kamermans, M., and McMahon, D.G.
- ID
- ZDB-PUB-120227-7
- Date
- 2012
- Source
- Journal of neurophysiology 107(10): 2624-2632 (Journal)
- Registered Authors
- Kamermans, Maarten, McMahon, Douglas
- Keywords
- retina, gene expression, patch clamp, connexin, feedback
- MeSH Terms
-
- Animals
- Animals, Genetically Modified
- Connexins/genetics
- Connexins/metabolism*
- Electrical Synapses/physiology*
- Gap Junctions/metabolism
- Membrane Potentials/physiology
- Retinal Horizontal Cells/physiology*
- Synaptic Transmission/physiology
- Zebrafish
- Zebrafish Proteins/genetics
- Zebrafish Proteins/metabolism*
- PubMed
- 22357795 Full text @ J. Neurophysiol.
Connexin channels mediate electrical synaptic transmission when assembled as cell-to-cell pores at gap junctions and can mediate transmembrane currents when expressed in plasma membranes as hemichannels. They are widely expressed in the vertebrate retina where in electrical synapses they are critical for transmission of visual signals. While the roles of connexins in electrical synapses are well-studied, the function and roles of connexin hemichannels in the nervous system are less well understood. Genetic deletion in zebrafish of Cx55.5 alters horizontal cell feedback to cones, spectral responses and visual behavior. Here, we have characterized the properties of hemichannel currents in zebrafish retinal horizontal cells and examined the roles of two connexin isoforms, Cx55.5 and Cx52.6, that are co-expressed in these cells. We report that zebrafish horizontal cells express hemichannel currents that conduct inward current at physiological negative potentials and Ca2+ levels. Manipulation of Cx55.5 and Cx52.6 gene expression in horizontal cells of adult zebrafish revealed that both Cx55.5 and Cx52.6 contribute to hemichannel currents; however, Cx55.5 expression is necessary for high amplitude currents. Similarly, co-expression of Cx55.5 with Cx52.6 in oocytes increased hemichannel currents in a supra-additive manner. Taken together these results demonstrate that zebrafish horizontal cell hemichannel currents exhibit the functional characteristics necessary to contribute to synaptic feedback at the first visual synapse, that both Cx55.5 and Cx52.6 contribute to hemichannel currents, and that Cx55.5 may have an additional regulatory function enhancing the amplitude hemichannel currents.