Variation in resitance head

Hello again!

Has anyone had any experience with the resistance check reporting large electrode resistance > 2 MOhm only to find that moving the electrode out of the solution and putting it back in can result in the resistance dropping to 200-300 kOhm (which is normal for us)?

Is this some junk on the end of the electrode and should we ignore it or should we alter our script to move in and out of the well if the resistance is greater than 1 MOhm or so?

thanks again

steve

Hi Steve,

when does this happen? At the first oocyte e. g. after night or also during a run?

Ciao,
Mike

Bayer Technology Services / Electrophysiology

Hi Mike

It happens during a run and not just for the first well. There could be 6-7 good recordings in a row with low resistance, and then one will be much higher, we have written to code to ingnore this else the run would stop too frequently and we found that the next well the resistance would return to normal. I assume it something blocking the tip that clears itself and I wanted to know if anyone else had this experience. Right now if we are watching the run we will stop the script after the resistance check got to manual mode and lift the recording head out of the well and simply put it back in and that seems to fix our resistance problems. Its not the well depth as we have checked that we have full immersion. Ignoring the problem completely does not always work as sometimes we dont get a stable offset correction if the resistance is too high.

Steve

Hi Steve,

>>>Right now if we are watching the run we will stop the script after the resistance check got to manual mode and lift the recording head out of the well and simply put it back in and that seems to fix our resistance problems.<<<

If that is enough, try this:

# initial part of the script
set $VAR_minResistance:=100
set $VAR_maxResistance:=1000


# your script
# ...


# resistance check (measuring head is in the liquid!)

# 1. try
wait 2000
get_resistance
message "Electrode resistance is " $RESISTANCE " kilohms"
if $RESISTANCE not_between $VAR_minResistance and $VAR_maxResistance then next
begin_if
message "Electrode impedance is not in the range."
message "1.try to clean ..."
# can also be repeated several times with a for - loop
# maybe you have to adjust the parameter after step_up (here 5mm)
zmove step_up 5000
wait 500
zmove well
end_if

# 2. try
wait 2000
get_resistance
message "Electrode resistance is " $RESISTANCE " kilohms"
if $RESISTANCE not_between $VAR_minResistance and $VAR_maxResistance then next
begin_if
message "Electrode impedance is not in the range."
message "2.try to clean ..."
zmove step_up 5000
wait 500
zmove well
end_if

# 3. try
wait 2000
get_resistance
message "Electrode resistance is " $RESISTANCE " kilohms"
if $RESISTANCE not_between $VAR_minResistance and $VAR_maxResistance then next
begin_if
message "Electrode impedance is not in the range."
message $VAR_resistanceCheck ".try to clean ..."
zmove step_up 5000
wait 500
zmove well
end_if

# final check
wait 2000
get_resistance
message "Electrode resistance is " $RESISTANCE " kilohms"
if $RESISTANCE not_between $VAR_minResistance and $VAR_maxResistance then stop
begin_if
message "Electrode impedance is not in the range."
speak "Please replace the measuring head."
end_if

I haven't tested it, only syntax check. First I tried the waitfor - loop, but it works in the moment only with the $VALUE (-> new feature request in the bugtracking). So I have to use these four if - blocks.

This code is ideal for macro! (You can use it in nearly all scripts.)


Ciao,
Mike

Bayer Technology Services / Electrophysiology

Dear Steven, dear Mike

It seems that the electrode tips may get clogged after some impalements. This effect seems to increase with a bad oocyte performance, maybe because the tips get clogged by cell debris.

Unfortunately, there is a problem with the measurement of the resistance when the impedance is high (above 1 MOhm). Sometimes, the amplifier measures a much lower resistance (in the normal range or sometimes even lower) in this case. This means, that it is most likely that the high values you get are correct, and the low ones are not.

This problem will be solved with the next amplifier version. Meanwhile, you can record with a measuring head even if the resistance is higher than recommended as long as the clamp is still stable. Sorry for this inconvenience. You can check the voltage clamp in the script as follows. I have not tried this piece of code yet with real oocytes, so maybe you have to repeat the If Condition a few times to see whether the clamp remains stable.

holding voltage -80
clamp voltage

lt_recording on
message "Testing voltage clamp ..."
wait 1000
lt_recording off

if $VOLTAGE not_between -85 and -75 then stop
begin_if
message "Voltage clamp at " $VOLTAGE " mV = not stable, please replace measuring head."
end_if

message "Voltage clamp ok at " $VOLTAGE " mV."

Best regards, Christine (MCS)

Hi there Steve.

We have observed this problem with a customer and it was resolved by changing the oocytes. It would appear that if the oocytes are not in tip top condition they tend to block the tips more easily - they tend to be quite sticky. The new batch of good oocytes did not block the electrodes and resistances were back in the kOhm range.

Regards, Nick.