membrane_props.md

Membrane properties analysis

Man Ho Wong
Xu Lab, Department of Neuroscience, University of Pittsburgh.

This page documents the algorithm of membrane properties analysis, which is implemented through the function membraneProps.m.

Steps

1. Zero every trace

Zero every trace of capacitance transient by the average amplitude of its own baseline (defined by the user, e.g. 0 to 4 ms of the trace).

2. Get the average trace

3. Determine transient peak direction by test pulse direction

4. Find the peak location

The location of the first transient peak is defined as the first sampling point with either minimum or maximum value depending on peak direction.

5. Locate the decay window

The decay window is defined as the decay from the peak location to the user-defined end point (this depends on the length of test pulse).

6. Zero the trace in the decay window to the stable current

The stable current ($I_{stable}$) is the difference between the baseline and the last 10 sampling points of the decay window.

7. Fit decay to a first-order exponential function

The trace within the decay window is fitted to a first-order exponential function using the non-linear least squares method. The function is shown below:

$I=I_0\cdot e^{-t/tau}$

where $I_0$ is the initial current (i.e. peak).

8. Compute passive membrane properties

The decay time constant (tau) is obtained directly from the fitting result. Other passive membrane properties are defined as follows:

$R_{input}=V_{testpulse}/I_{stable}$

$R_{series}=V_{testpulse}/I_{peak}$

$C_{membrane}=tau/R_{series}$

where

$R_{input}$ = input resistance

$R_{series}$ = series resistance

$C_{membrane}$ = membrane capacitance

$V_{testpulse}$ = test pulse size

$I_{stable}$ = stable current (see step 6)

$I_{peak}$ = peak current