The name is absent

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photocurrents electrical signal as it propagates from the outer segment to the synapse. On-
cell patches typically showed 1/14 as many channels as the whole cell. We estimate that the
average surface area of rod and cone inner segments are 586 and 508 μm², respectively, from
analysis of salamander retinal tissue sections [114]. Assuming the channel density is even
throughout the inner segment, this would correspond to a density of 3.6 channels per μm²
in rods, and 4.0 channels per μm² in cones. These estimates of HCN channel density in
the inner segment of rods and cones are similar to results reported by cell-attached currents
recorded from areas near the soma of rat cortical neurons [66]. Kole et al report that HCN
channel varies exponentially from 9 - 550 channels per μm² progressing from the soma to
the distal end of the dendrites, an effect that had been previously noted in hippocampal
pyramidal neurons [74].

3.3 FunctionofHcNchannelsinphotoreceptors

3.3.1 Simulated HCN current during rod light response

In order to determine HCNl channel contributions to light evoked responses in photore-
ceptors, we simulated the light response of a rod photoreceptor, incorporating the data from
our single channel conductance and whole cell studies of HCN1 channels (described above)
into the simulation (figure 3.4 A). The numerical simulation model was developed with pho-
tocurrent data from the suction electrode technique experiments of Baylor et al [18], and our
HCN channel data combined with models of other voltage gated currents, as developed by
other salamander rod photoreceptor models [64, 73, 86, 88]. The simulation approximates

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