Multichannel Systems HiClamp Manual - Manual (Page 63)

Troubleshooting
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Data can be fitted using the typical procedure of selecting the desired curve, selecting the
initial parameters, and activation of the curve fitting procedure. Data are fitted using a single
Boltzman equation. Note that results of the curve fitting are applied to the IV curve allowing
to compare the result of the fit with the data.
Plot of the conductance for KV1.4 and curve fitting
In the second case the current evoked by a voltage step is measured at the very beginning of
the relaxation curve. This second method offers the advantage of a direct measurement of the
current without requirement of the blockade by a selective inhibitor. Positioning of the crosshair
is adjusted after a blow up of the section of interest using the magnifying tool.
Positioning of the cursor on the relaxation tail
Note that the blue cursor is placed where the current is measured, the cyan (min value)
towards the end of the recording and the dark blue in the voltage window at the
position of the voltage step that activated the KV1.4 current and selection of Min-Max.
Results are obtained as described above for the activation steps and yielded comparable
activation profiles. The main advantage of this second procedure is to allow measurements
at a fixed potential and thereby alleviate the needs for the subtraction of traces in presence
of a blocker. This method is often used to characterize the voltage activation or blockade of
K-channels such as HERG channels. Measurement of the relaxation current at a fixed potential
is also often used for the characterization of blocking agents (Windisch et al., 2011).