Gap junctions between horizontal cells in the cyprinid fish alter rapidly their structure during light and dark...

The dynamics of the structure of gap junctions between outer horizontal cells (HCs) and between their axonal terminals in the retina of the goldfish during light and dark adaptation is described by means of quantitative freeze-fracture replica examination. The light adaptation was performed in red light. In dark-adapted retinae the gap junctional connexons are arranged much more dense than in light-adapted retinae. The rearrangement during the first minutes of light adaptation proceeds faster than during the first minutes of dark adaptation. Since dark adaptation is accompanied by surround enhancement and presumably by coupling of HCs it is concluded that densification of HC gap junctions may correlate with coupling, and scattering of HC gap junctions with uncoupling of this type of electrotonic synapse.