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
μM, −9% reduction in coupling) and dopamine (100–300
μM, −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.