PH-GATED DOPAMINERGIC MODULATION OF HORIZONTAL CELL GAP-JUNCTIONS IN MAMMALIAN RETINA

Horizontal cells mediate lateral inhibition in the outer retina, and t his process is dependent on electrical coupling through gap junctions, giving rise to receptive fields that are much wider than the dendriti c fields. This study on rabbit retina shows that the permeability of t he gap junctions between A-type horizontal cells, as assessed by Lucif er yellow dye coupling, is modulated by dopamine through a D-1 recepto r linked to adenylate cyclase. Both exogenously applied dopamine and e ndogenously released dopamine uncoupled the horizontal cells, but the effect was pH-gated whereby it occurred only at an extracellular pH 7. 2 +/- 0.05. The horizontal cells also uncoupled in acidic media (pH 7. 0 or below) in the absence of dopamine. Our results show that horizont al cell coupling in the mammalian retina is regulated by both dopamine and pH. Given that the pH in the outer retina varies with the metabol ic activity of the photoreceptors, these results suggest that ambient light conditions could gate the activity of neurotransmitters through pH-sensitive mechanisms.