The name is absent

21

time constant around 50 ms at -104 mV, which would yield a minimum filter time constant
of 200 Hz. We therefore chose a 400 Hz digital cutoff frequency in order to reduce back-
ground noise while still preserving HCN kinetic information. See Kole et. al, 2006 for an
analysis of single HCN channel estimates vs filtering frequency.

The single channel conductance (7) number of channels (jV) present were estimated by
fitting a plot (figure 2.2 C, D) of the ensemble variance vs the mean current (figure 2.2 B)
with equation 2.4. к represents the variance offset from underlying noise that is not time
dependent, and was subtracted out in displayed plots (figure 2.2 C,D).

T²
σ²(I) = 7I - — + к                          (2.4)

2.6 Numerical Methods

Simulations were computed in MATLAB (Mathworks) using the ode 15s numerical solver.
The differential equations and constants for the model are given in appendix 1. Equations for
voltage gated channels come from studies previously published by Liu and Kourennyi with
the Ih model as published by Barnes and Hille [73, 13]. Although more accurate models
of HCN channel kinetics exist, [2] the Barnes model describes Ih kinetics relatively well
(unpublished data), and requires only one state variable, greatly decreasing computational
complexity. Equations and constants for the photocurrent come from studies by RD Hamer,
originally from Nikonov et al. [51, 85]. Initial conditions for the model were determined by
allowing the system to relax to steady-state without any light input.

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