Saturday, March 18, 2006

Biological electric fields

Many living cells keep their interior at a different voltage than their exterior.  The upper limit for human cells seems to be about 50 millivolts.  Normally we think of that as a puny voltage—a flashlight battery is 30 times higher.

But I got to thinking.  Sure, the voltage is smallish, but cell membranes are super thin, in the range of 5 nanometers.  If we divide the voltage by the distance it acts over, we get the electric field strength:

        50 mV / 5 nm = 10 000 000 V/m

Good grief, that is big!  (The dielectric breakdown strength of air is a couple of MV/m.)  So cell polarization is not a subtle force that gently touches trans-membrane proteins.  It is definitely more of a fold-spindle-mutilate interaction.  I am impressed that ion transporters can pump against a potential gradient that large.


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