38
-500 -⅛----------1----------1----------1----------1∣- -100
Hz
Figure 3.5 : Stimulus and response of a rod (Al) and cone (Bl) to a frequency chirped
sine wave current stimulus. Rod (A2) and Cone (B2) frequency response determined from
stimulus and response, plotted on log-log axes. Application of ZD 7288, which blocks HCN
channels, is shown in red. Normal rods and cones are seen to have a peak frequency response
near 4 Hz. HCN channel block is seen to abolish the band-pass filter characteristic, leaving
a low-pass filter resulting from the membrane capacitance and resistance.
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