Abstract
Retinal amacrine cells (ACs) regulate activities of retinal ganglion cells, the output neurons to higher visual centers. Homologous electrical synapses between ACs contribute cellular mechanism of lateral inhibition in the inner plexiform layer. Lateral inhibition was expected to depend on functional coupling by electrical synapses. The fraction of open channels in gap junction plaques was evaluated with techniques of dual patch-clamp recordings, intracellular labeling, connexin immunocytochemistry, and high-voltage electron microscopy. Electrical junction conductance in cell pairs was measured by dual patch-clamp recordings. High voltage electron microscopy (Hitachi 1250M, NIPS, Okazaki, co-operative program 2006-HVEM13) measured the size of gap junction plaques localized between the dendrites of Neurobiotin-coupled cells. In confocal laser-scanning imaging, connexin localization counted homotypic gap junction connections. Assuming the density of connexons by freeze-fracturing methods and measured single channel conductance, the conductance of each gap junction plaque was expected. The presence of junctional connections between a cell pair will lead to estimate a total intercellular junctional conductance. The measured conductance could allow to estimate a fraction of functional channels in a gap junction plaque. The open channel fraction may be on the order of 1 in 10, which was compatible to that of alpha retinal ganglion cells (Hidaka et al., J Neurosci, 24, 2004). [J Physiol Sci. 2007;57 Suppl:S109]
