The name is absent

57

I_Kx has also been shown to be involved in high-pass filtering of rod light responses, espe-
cially responses to dim stimuli [19]. Iχ_x is similar to the М-current in neurons in that it is a
potassium conductance that is partially activated at resting potential, is further activated by
depolarization, and is largely non-inactivating [67] . Kx channels also appear to be similar
to EAG and Kcnv2 potassium channels, but its exact molecular origin is presently unknown
[47,27]. While both I_Kx and 7⅛ are known to mediate high-pass filtering in rods, an impor-
tant difference between the two is that during a light response (in which the rod membrane
hyperpolarizes), Kx conductance decreases, while h conductance increases. Due to their
different reversal potentials (-30 mV for I_h and -75 mV for Iκ_x)> the net current change
caused by I_h and I_Kx gating is inward during a light response, tending to counteract the ini-
tial hyperpolarization phase of the response [54,19]. This reactive depolarizing effect leads
to high-pass filtering of the input signal.

4.1.2 Results

To extend our previous studies of the h-current, we examined the contribution of I_h to the
rod light response when the Kx conductance, calcium conductance, and other potassium
conductances are blocked. To do this, we recorded the rod light response with 5mM Co, 5
mM Ba and 20 mM TEA present in the bath [10, 43, 54]. Five flashes of light of increasing
intensity were delivered to a rod and the voltage response was recorded. Then I_h was blocked
with 50 μM ZD7288 and light responses were recorded again.

In the presence of Co, Ba, and TEA, the rod’s light response is smaller and occurs from a

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