Dear Bill,
I have a couple of tricks that I use to reduce both the electrical
noise and the changes in bath solution level. Rather than use a very
high suction rate to break-up the solution into beads, I place a
bubble trap close to the microscope stage, with a short length of
tubing going to suck solution off from the bath. The bubble trap is
nothing special - a cut-down 5 ml syringe with a rubber stopper in
the open end and a hypodermic needle going through the stopper. That
way there is a luer fitting on each end to connect the tubing. The
important aspects are 1) to keep the line from the bath to the bubble
trap short, and 2) to keep the bubble trap close to the grounded
(shielded) environment of the stage. I usually find that placing the
bubble trap just below the level of the stage and towards the rear is
a good position. We've used several methods of attaching the bubble
trap, including velcro (the velcro with adhesive on one side) and
sometimes there is a convenient structure to strap the bubble trap to
with cable ties.
The second trick is having a sloping surface at some location that
enters the bath and then locating your suction pipe so that it sits
flush (parallel) to this sloping surface and just comes into contact
with the solution. This setup uses surface tension to your advantage
rather than trying to work against it. I haven't played around a lot
with the angle of the sloping surface; I use around 40 deg above the
horizontal.
With both these tricks I find that I can get away with a much less
powerful suction and still get efficient solution exchange.
This works for me, but like a lot of things in electrophysiology,
there is always more than one way that works.
Good luck.
Trevor Lewis
