The modulation of intercellular coupling in the retina.

Gap-junction coupling between retinal neurons of the same (homologous) or different (heterologous) type can be modulated dynamically by neurotransmitters and by the level of ambient illumination. The homologous coupling of both horizontal cells and rod (AII) amacrine cells is reduced by dopamine, but there appear to be cell and species differences in how the ambient illumination interacts with the dopaminergic system to modulate the coupling. Both the homologous coupling of horizontal cells and the heterologous coupling between AII amacrine cells and cone bipolar cells are reduced by nitric oxide, but it is not known if changes in illumination modulate coupling through an endogenous nitrergic mechanism. The heterologous coupling between rod and cone photoreceptors is modulated by illumination, but the endogenous mechanism has not been identified.