Electrical coupling of retinal horizontal cells mediated by distinct voltage-independent junctions.
Electrical coupling between H2 horizontal cell pairs isolated from the hybrid bass retina was studied using dual whole-cell, voltage-clamp technique. Voltage-dependent inactivation of junctional currents in response to steps in transjunctional voltage (Vj) over a range of +/-100 mV was characterized for 89 cell pairs. Approximately one-quarter of the pairs exhibited strongly voltage-dependent junctions (>50% reduction in junctional current at +/-100 mV), another quarter of the pairs exhibited voltage-independent junctional current (<5% reduction at +/-100 mV), and the remainder of the pairs exhibited intermediate values for voltage inactivation. We focused on further characterizing the Vj-independent junctions of horizontal cells, which have not been described previously in detail. When Lucifer Yellow dye was included in one recording pipette, pairs exhibiting Vj-independent coupling showed no (9/12), or limited (3/12), passage of dye. Vj-independent coupling was markedly less sensitive to the modulators SNP (100-300 microM, -9% reduction in coupling) and dopamine (100-300 microM, -6%) than were Vj-dependent junctions (-45% and -44%). However, simultaneous application of both SNP and dopamine significantly reduced Vj-independent coupling (-56%). Both Vj-independent and Vj-dependent junctions were blocked by DMSO (1-2%), but Vj-independent junctions were not blocked by heptanol. Single-channel junctional conductances of Vj-independent junctions range from 112-180 pS, versus 50-60 pS for Vj-dependent junctions. The results reveal that Vj-independent coupling in a subpopulation of horizontal cells from the hybrid bass retina is mediated by cellular junctions with physiological and pharmacological characteristics distinct from those previously described in fish horizontal cells.
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Department of Physiology, University of Kentucky, Lexington 40536-0084, USA.
Zhang
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McMahon
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D000818:Animals; D001492:Bass / Q000502:physiology*; D002478:Cells, Cultured; D004121:Dimethyl Sulfoxide / Q000494:pharmacology; D004298:Dopamine / Q000494:pharmacology; D017629:Gap Junctions / Q000187:drug effects / Q000502:physiology*; D019850:Heptanol / Q000494:pharmacology; D009599:Nitroprusside / Q000494:pharmacology; D018408:Patch-Clamp Techniques; D012160:Retina / Q000166:cytology / Q000187:drug effects / Q000502:physiology*; D009435:Synaptic Transmission / Q000187:drug effects / Q000502:physiology
D009599:Nitroprusside; D019850:Heptanol; D004298:Dopamine; D004121:Dimethyl Sulfoxide