Hi
When I am recording hERG current, always the current shows rundown. How you guys take it into account for the assay?

Some people include PIP2 in the patch pipette. You will need to sonicate this into your pipette soln immediately before each patch.

Another way is to run your proptocol for at least 10 sweeps before drug application and get a fit of the tail currents during ths time. Extrapolate the fit over the duration of the whole experiment and normalize you tail currents in the presence of drug to this fit.

There is a useful paper describing a computer algorithm called I_VOC which deals with current run down. Reference: Marrannes - ComputerMethods&Programs in Biomedicine (2004) v74 page 167. You dont need the actual program to do the run down compensation.. I can do it offline easily using pclamp and Origin graphing software.

Many labs state that if the rundown is more than 10% of the starting peak amplitude then they don't use the cell. The problems is that you will have hardly any data if you do this. However, ensure that your cell has a resting membrane potential before and after your drug application and that you have not just killed it.

Current voltage relationship of hERG peak tail current shows S-shape curve. From I=V/R, current amplitude seems to be liniealy increased at higher voltage, if R does not increase. But the current amplitude reaches to the max around 0 mV and no more increase. Why V/R is constant at higher voltage? Maybe I am completely misunderstanding??
Thanks