Once again with the frog pee

[rebeccmeister]

Today's labs are supposed to be all about membrane transport across frog skin. Getting all the moving pieces set up has been a huge project. Ordeal. And then...we crashed and burned this morning.

I couldn't quite tell what the full cause was, but my instinct told me to just let the students go instead of making them fight with the instrumentation, so I did. So then there's always the worry that the decision was premature and we could have fixed things, and there went that learning opportunity.

But as I think it over, the thing is, we weren't detecting a sufficiently large charge difference or current across the frog membranes we're working with. I've now had time to revisit notes from trying this in Arizona, and that has confirmed my suspicion.

I'm still going to make the afternoon lab go through the whole setup process, as we will still learn a few things by doing so, and then we can test some other things out instead. But I'm going to have to run a few more tests before trying this lab again next year.

One of our biggest challenges this semester has been trying to adapt labs I did previously with bullfrogs, to much smaller spotted leopard frogs. I'd like to be able to keep using the spotted leopard frogs, but on the other hand we keep on being at the extreme low end of what our instrumentation can detect and measure.

Comments

[randomdreams]

This is the polarization potential, using a patch clamp?
That's in the tens of millivolts, right? What sort of instrumentation do you have?
I ask because stuff that's above like 100 microvolts is stuff I could build a whole bunch of cheap opamps with like x20 gain and adjustable offset so you could trim them down to sub-1mV offset, and you could stick them between your probe and your instrumentation.

[(Anonymous)]

Yes, this is that. We can do down to hundredths of millivolts with our stimulator and recording setup. But we're using multimeters to record microamps, and that's where we think we were running into difficulties with instrument sensitivity.

But somehow the afternoon lab had much greater success. I think what I'm going to have to do is set up and test the whole setup thoroughly ahead of the lab next spring - maybe about a month in advance so I have enough time to work out the kinks and troubleshoot. All told, it's still a super-cool lab. The students have a hilarious reaction, though, when they realize that I've snuck in some physics among the biology, heh.

[rebeccmeister]

Whoops, prior comment was me, not logged in...