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.