The name is absent

18

2.5 Data analysis

Data Analysis was performed with Igor Pro or MATLAB using custom written and standard
built-in routines.

Non-Stationary Fluctuation Analysis

Nonstationary Fluctuation Analysis (NSFA), sometimes called Nonstationary Noise Anal-
ysis (NSNA) was used to estimate the conductance of single HCN channels [61, 91, 95].
This technique uses many repeated command voltage pulses to create a collection of many
current responses. This collection of traces is referred to as an ensemble. From this ensem-
ble, the variance and mean current can be computed at each point in time using equation
2.2. A plot of the variance versus the mean was used to estimate the single channel con-
ductance by fitting with a parabola. We use software routines written in Igor Pro for the
NSFA. For our experiments, NSFA was performed on a series of IOO or more data traces
pulsed to no more than -94 or -104 mV in order to avoid dielectric breakdown of the mem-
brane. Ideally the noise analysis should be performed using a command pulse that can both
fully activate the ion channel of interest and generate sufficient driving force for the current.
However, photoreceptor cell membranes experience dielectric breakdown beginning near
-IOO mV [44]. Dielectric breakdown manifests itself as a transient high amplitude 1/f noise
process, invalidating the fluctuation analysis in traces where it is present. Therefore we had
to use a less hyperpolarized voltage in order to achieve recordings uncorrupted by mem-
brane breakdown. As a result, our NSFA estimates could achieve a maximum Po=.95∕.85

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