55
Chapter 4
Functional Models of the Rod and Cone
4.1 Interactions between 7⅛ and Iκx in the rod light response
4.1.1 Introduction
During a photoreceptor light response many simultaneous membrane currents are summed
by the cell to generate the voltage response. In turn, the voltage change of the cell alters the
gating of each conductance through the voltage sensors of the channel. Through this non-
linear action of voltage on gating, and the action of gating on voltage, different classes of ion
channels influence one another’s activity. Therefore, it is generally imprecise to classify the
function of a single class of ion channel in a neuron outside the context of its peers. In this
research addendum we describe one such interaction between Ih, mediated by HCNl chan-
nels, and Iχx, mediated by M-Iike potassium channels [107, 67] in influencing the mem-
brane impedance of a rod during its light response.
In our work on HCN channels in salamander photoreceptors, we characterized their bio-
physical properties and investigated their functional role in tiger salamander (ambystoma
tigrinum) rods and cones [14]. From investigations of the gating kinetics and immunohis-
tochemical staining, we showed that HCNl channels are responsible for the Ih current ob-
served in these cells. We used the HCN antagonist ZD7288 to block HCN1 channels in rods
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