Dopamine Decreases Conductance of the Electrical Junctions between Cultured Retinal Horizontal Cells

Horizontal cells from the white perch were isolated by enzymatic treatment and trituration of the retina and were maintained in culture for 1-5 days. Overlapping pairs of horizontal cells were identified, and the two cells were recorded from simultaneously, using whole-cell patch clamp techniques. Electrical coupling between cells was determined by passing current pulses into one cell, the driver cell, while (i) recording voltage changes in the other, follower cell, or (ii) measuring current flow into the follower cell. Most cell pairs of the same morphological type were coupled electrically, with coupling coefficients often >0.9. Junctional resistance was typically found to be between 20 and 60 MΩ and junctional conductance was between 150 and 500 nS. After application of 1-μ l pulses of dopamine (200 μ M) to coupled pairs of cells, the coupling coefficient fell to ≈ 0.1, junctional resistance increased to 300-700 MΩ , and junctional conductance decreased to 15-30 nS. Recovery of coupling took, for most cell pairs tested, 8-15 min after dopamine application. The exogenous application of 8-bromo-cyclic AMP (0.5-1 mM) also caused uncoupling of horizontal cell pairs; however, neither isoprenaline nor L-glutamate altered coupling significantly.