Photochemical Observation of Ion Flows in Membrane Channels

摘要

Laser Doppler velocimetry is applied to a study of the synchronous motions ofions in membranes and membrane channels. The technique provides direct measurements, for example, of local velocities within gramicidin channels and these measurements can be used to elucidate the kinetic mechanism of ion flows in such channels. The laser Doppler experiments yield data which suggest that ion motions in the channel are regular, i.e. the ions move at a steady velocity with some fluctuations about this velocity due to the molecular structure of the channel. Standard electrochemical measurements give no detailed information about such motions within the channels and, because of this lack of information, many multiparameter mechanisms have been postulated to describe the intrachannel kinetics. Since the number of 'fitting' parameters is often large with respect to the available data, many models can be fitted to the data and it is extremely difficult to prove a permeation mechanism. With the detailed velocity distribution for ions in the channel, it becomes possible to differentiate the various mechanisms for ion permeation and develop a consistent mechanism for ion permeation in a specific channel.