81
The I-V relationship for the current flow between two rods is shown in figure 5.4 C. The
black line shows the value of the initial transient current flow in the follower cell. This is
thought to represent the current flow due to electrical coupling between the cells through
the network. The red trace shows the steady-state value of the current flow, which occurs
after voltage gated ion channels have altered the current flowing though adjacent cells. The
current flow through directly from driver to follower cell should not be affected by gating of
currents because these cells are held voltage clamped. However, adjacent cells do not have
their membrane potentials clamped, and therefore the voltage of the driver cell will alter the
current flow through these adjacent cells as this voltage causes a gating of ion channels. The
difference between the initial and steady-state values shows the importance of the indirect
current flow through the network.
The I-V relationship between the two cells was linear in both the initial and steady-state
phases, except at very hyperpolarized votlages, where Ih is active in adjacent cells, and at de-
polarized voltages, where voltage gated potassium channels activate. This is evidence that the
gap junctions between cells are purely resistive, and do not have voltage dependent changes.
The average network resistance between all cells recorded was 890 ± 10 MΩ (SEM) from
the initial current, and 1120 ± 13 MΩ from the steady-state current. Most of the recordings
were made between pairs of cells, reversing which cell was the driver and follower cell. In
order to directly compare our results with previous measurements of rod-rod conductance
[115], the results were tabulated as conductances rather than resistances. Table 5.3 shows
the conductance values for recordings made in each pair. Analysis of Variance (ANOVA)