The name is absent

30

mouse HCN3 is 85 kDa. Our results using immunohistochemical labeling and western blot
of whole retina, while they cannot rule out the presence of other HCN isoforms, are sup-
portive of our electrophysiological findings that HCNl is the dominant isoform present in
photoreceptors.

3.2.3 HCNl single channel conductance

With evidence from whole cell currents and immunohistochemical experiments indicat-
ing that the identity of the ∕⅛ current in rods and cones is the HCNl channel, we endeav-
ored to estimate the conductance of single HCNl channels in the whole salamander retina.
Normally the conductance of single ion channels is determined by directly observing single
channel events with a cell-attached patch, but the conductance of HCN channels is so small
that it is below the thermal noise threshold of any physically realizable patch clamp amplifier.
Therefore we used a statistical technique called Nonstationary Fluctuation Analysis (NSFA)
to estimate the conductance of single HCN channels in vivo [4, 53, 95]. An ensemble of
IOO traces was recorded from whole cell currents from rods using 100 traces of a command
pulse to -104 mV (as in figure 3.3 A), with other channel activity blocked with special exter-
nal solutions (see Solutions in Methods). The variance and mean of the ensemble were then
computed (as in figure 3.3 B) (see Methods for detailed explanation) and plotted against
one another (figure 3.3 C2). We initially used a whole-cell patch as opposed to the more
common cell-attached technique in order to maximize the Ih current recorded. With this
whole-cell NSFA recording technique, we estimated the HCN channel conductance to be

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