Ion channels are proteins with a hole down their middle that perform an
enormous range of biological functions, from information processing in the
nervous system to control of muscle contraction. The properties of ion
channels, like many proteins, are dominated by the electrostatic energy of the
ions in their 'active site' and the excess free energy necessary to crowd ions
into that pore. Ions in channels (and bulk solution) are a compressible plasma
(although the solution they are in is incompressible) and so the basic physical
laws are known. The channel contributes a specific density of fixed charge,
excluded volume, mechanical strength, and dielectric environment. Each of
these variables needs to be determined by a combination of structural
measurements (e.g., x-ray cystallography), functional measurements (e.g.,
single channel recording of ionic currents), theory, and simulation.
Determining each of these variables is an inverse problem of considerable
importance: once each is known (or bounded), natural proteins can be
modified and new proteins can be sythesized to do what we wish.
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