Temperature and voltage clamp

kenneth collins kenneth.p.collins at worldnet.att.net
Fri Nov 12 13:39:47 EST 2004

"Matt Jones" <jonesmat at physiology.wisc.edu> wrote in message 
news:b86268d4.0411120955.61401a81 at posting.google.com...
|r norman <rsn_ at _comcast.net> wrote in message 
news:<vksuo09mt3f9oldt02gmp7n7nl9jsjq78n at 4ax.com>...
| > On Mon, 08 Nov 2004 07:53:47 GMT, BilZ0r
| > <BilZ0r at TAKETHISOUThotmail.com> wrote:
| >
| > >Hi,
| > >I was talking to a colleague today, who primary studies 
antiepileptics with
| > >voltage clamp on voltage sensitive sodium channels expressed in 
X. Oocytes.
| > >He told me he does all of his work, I believe, at 15ºC... Does 
that sound
| > >right?
| > >
| > >Why would he use such a low temperature? So he could see any 
effects of
| > >gating more readily? Any ideas?
| >
| > Why do you think 15 C is a "low" temperature?  Remember, the 
work is
| > done on Xenopus cells, not mammalian.  Xenopus ordinarily lives 
| > temperatures of 15 to 25 C.  Preparations do last longer and 
remain in
| > better conditions at cooler temperatures.
| Good point.
| On the other hand, the sodium channels he studies are probably
| mammalian, e.g., rat, mouse or human. So one could still argue 
| this is a lower temp than what those channels see in their native
| state (which is obviously not in a frog egg, but that's another
| story).
| However there's quite a long history of people studying sodium
| channels at low temp, even right down to 4 deg C.  I think the 
| reason for this is that sodium channels have really really fast
| kinetics, which causes problems for accurately recording their
| properties. For example, the temporal resolution of an experiment 
| ultimately limited by the sampling rate, which is usually limited 
| <100 KHz in standard acquisition systems. Then one needs to filter 
| the Nyquist freq or below, which brings the resoltution down to 
| kHz at best. Actually that's probably not enough filtering to get 
| of enough noise, so in practice people will usually be working at 
| Khz. This means that components of the signal faster than about 
| microseconds will be distorted or lost. At room temp or 35 deg C, 
| currents can probably have rise times faster than 100 us, so they
| would be very badly distorted. Plus, aside from acquisition, in 
| to voltage clamp properly, the amp needs to be able to sense 
| changes and inject current faster than what the channel is doing,
| which is particularly problematic if the channel is trying to
| regeneratively alter the voltage (i.e., fire a spike).
| All of these problems are alleviated by lowering the temp, since 
| makes everything the biology is doing much slower.
| What i would worry about is whether all the transition rates of 
| channel vary with temperature in the same manner or not. If not, 
| the macroscopic behavior could actually be qualitatively different 
| low vs high temp.
| Matt

Your discussion nicely [and strongly] confirms
the stuff I discussed in the lnog-former "NL-P
Medicine" thread. One can see, in your dis-
cussion, a way to "interpolate" with respect
to inflamatory ["fever"] dynamics.


Cheers, Matt, ken 

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