Nerve membrane channel molecules undergo conformational changes during nervous activity. The propagated nerve impulse is a wave of transformation of molecular structure(s) in the membrane. Most functional properties of channels have been inferred from electrical measurements of current flowing through the channels or voltage changes arising from the current flow. The currents show the results of the change in structure; not the change in structure itself.

 

 

 

 In my lab, changes in the optical properties of nerves during the passage of nerve impulses have been measured. With voltage clamp experiments changes in birefringence have been associated with changes in sodium channels. There is a small decrease in the (linear) birefringence of nerves during action potentials. Birefringence is an indication of aligned material. The changes seen here are changes in alignment of elements that are radially aligned in the axon or perpendicular to the surface membrane.

In experiments with internally perfused, voltage-clamped squid giant axons, my lab has shown that most of this signal represents a conformational change of the voltage-dependent sodium channels. The experiments indicate about 10% of the channel molecule changes its orientation so that there are more peptide bonds more perpendicular to the membrane surface. The birefringence changes appear to be an optical expression of the same phenomena indicated by 'gating' currents, displacement currents that flow before the channels open. Recently, I have been studying agents that alter the gating currents.