Channel kinetics........

M.A. Tester mat10 at CUS.CAM.AC.UK
Tue Jul 5 13:43:35 EST 1994


Dear Cell Biologists,

This is a question to any channel people out there, from
a couple of plant electrophysiologists who have been working 
with single Ca channels for the past couple of years.

In our measurements of currents through these single channels,
we noticed little or no current reduction when we reduced (symmetrically)
the concentration of Ca, from 10 mM down to 1 mM. Intrigued, we
have gone to sub-millimolar concentrations, and find that the channel
appears to have an affinity for the transport of Ca which is somewhere well
below 1 mM. (This is even in solutions containing nothing other than
CaCl2, along with the inevitable 0.1 uM or so H+.)

We found this somewhat surprising, so we dug into the 
(all animal) literature to see if any of 'you guys' had made similar
measurements. To our surprise, we cannot find any paper in which
people have tried measuring single channel currents with Ca activities
below about 1 mM Ca. Surely we have missed something. Do any
of you know of such measurements; or why such measurements
have not been made?   (We are aware of measurements of Ca 
inhibition of Li fluxes [e.g. Kuo & Hess, 1993, J.Physiol. 466, 629]
which show a high affinity binding of Ca to the channel, but are
uncertain of the connection between this type of measurement 

of binding and our own measurement of conductance.


Any help with this will be greatly appreciated.



With many thanks for your time in reading this,

Yours sincerely,





Mark Tester & Miguel Pineros
Department of Plant Sciences,

University of Cambridge,

Downing St,

Cambridge, CB2 3EA,

U.K.

Tel. + 44 223 333918
Fax  + 44 223 333953




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