Noisy current trace during perfusion

Hi

We have been having a problem that surfaces from time to time and that is the appearance of electrical noise on the current trace. We have noticed that it is only apparent during the times when the perfusion and suction is running. If we stop the waterpump and the gpump (we only use the Gilson system) the noise completely dissapears. By eye the noise band is around 200 nA or so and is a nuisance. We dont see it with all recording heads and I wonder if it is anything we are doing wrong that can cause this problem?

Steve

Dear Steve

I can give you some general advise on this matter, but maybe some other users can give their opinion as well.

I suggest that you use some dye to stain the fluid so that you can actually see what happens in the well and tubing.

First of all, the fluid should run in the tubing from the outlet of the measuring head to the valve stand smoothly like a cord, with no interruptions. You will see that with the stained fluid. If this is not the case, there is something wrong with the perfusion. As you say, this is usually accompanied with high background noise, and also with an irregular sound, like slurping.

There are some possible reasons for that:

1. The design of the measuring head is not fully okay. This is especially likely if you see the problem only with some heads. Though MCS checks each single measuring head carefully under the microscope before delivery, slight variations in the geometries may have quite big impact on the noise performance. The distance between the perfusion tubes and the rim of the well could be unfavorable. If the perfusion tubes are too near to the well's rim, it may occur that the wells are sucked empty or that the liquid level shows strong oscillations. The tubes should be oriented straight down in the middle of a well. You may observe the same effect if the reference electrodes are too near the perfusion tubes. They should be bent more to the outside.
Also, please have a look at the z positions of the reference electrodes. If they are too near the liquid surface, you will have noise problems, too. They should be fully immersed.
Try to carefully rectify the positions of the tubes or the reference electrodes with a pair of tweezers, or replace the measuring head.

2. The waste bottle or the tubing connecting the waste bottle or pump are not the right type.
The system was optimized for this pump, the provided waste bottle, tubing and connectors. If you use other types, the vacuum maybe too weak or unstable. In your case, I am sure you have the provided stuff, but please check whether all connectors are tightly plugged and the system is airtight. The waste bottle should probably not be too full either.

3. The tubing from the outlet of the measuring head to the valve stand could have a leak somewhere. In this case, the aspiration would be unstable as well.

In summary, the applied vacuum is very important. It should be strong and stable. Minor irregularities could induce a big noise, even if the liquid level optically seems to be stable.

Best wishes from Germany, Christine

Hi Steve,

what happens if you use this measuring head in spite of the noise? Try measuring a complete plate with it. I find often that the noise decrease after some oocytes. (But don't ask me why!)


Ciao,

Mike

Bayer Technology Services / Electrophysiology

hi mike

We generally keep using them and as you say they do get quiter from time to time - i will try and see if that correlates with the slurping sound that christine suggested was the cause of the noise. for slow currents we just filter the noise in software.

steve