Ion velocity distributions in gramicidin channels determined with laser Doppler velocimetry.

Laser Doppler scattering from Tl(I) ions moving synchronously through an ensemble of gramicidin channels in a bilayer membrane gives their intrachannel velocity distribution. The observed velocity distributions are unimodal indicating that ion flow through some region or regions of the channels is relatively steady. Average intrachannel velocities range from 3.75 x 10(-2) m/s to 2.38 x 10(-1) m/s for transmembrane potentials between 10 mV and 150 mV, respectively.