Mechanical, thermal, and optical changes of the nerve membrane associated with excitation.

Abstract

In this minireview, some of the recent experimental findings on the excitable membranes of nerve fibers obtained by nonelectrophysiological means are discussed. This minireview, however, does not treat the vast literature on the "optical probes of the membrane potential," which is adequately covered by other excellent reviews [14,22,23,30,52].When the nerve fiber is excited, it transiently changes many of its physical properties. From the biological point of view, the most significant is the change in membrane potential, since the transmission of information along the nerve fiber is mediated by the electric local current. Other physical changes are significant mainly because they contain information on the molecular mechanism of the excitation process. They are usually very small for an easy detection, but progress in the techniques of extracting small signals from noise allowed us to discover and examine some of these signals. In this minireview, several recent findings on mechanical, thermal, and optical signals will be discussed.

Nonsynaptic and nonvesicular ATP release from neurons and relevance to neuron–glia signaling

“…This includes rapid heating and cooling [61–63], mechanical displacement of the axon membrane [64–76], and changes in light transmission through axons [77–84]. The rapid changes in light transmission and membrane displacement are caused by transmembrane flux of ions (notably Na + and Ca 2+ ) and water accompanying the action potential.…”

“…The rapid changes in light transmission and membrane displacement are caused by transmembrane flux of ions (notably Na + and Ca 2+ ) and water accompanying the action potential. This is believed to alter the submembrane cytoplasm and osmotic pressure, causing submicroscopic axon swelling, which reduces light scattering through axons [78,84,85]. Flexoelectric deformation of curved cell membrane can also contribute to membrane displacement during excitation [86].…”

Signaling by Neuronal Swelling

“…Electrical excitation of nerve axons also produces many other effects (1–3), including rapid heating and cooling of the axon (3–6), volume changes in the axon (6–14), and changes in the optical properties of the axon that alter the transmission of light, its polarization, and scattering (15–22). This set of movies shows optical changes, and physical displacement of axons that occur when neurons fire action potentials, as well as a nonsynaptic mechanism of signaling that occurs as a response to the physical changes: the release of the neurotransmitter ATP through membrane channels.…”

Chloramine-T alters the nerve membrane birefringence response

“…The underlying changes in specific ion permeability control the electrical currents which cause the action potential to be self regenerating and propagating, supporting its information-carrying role in the cell (Hodgkin & Huxley, 1952). Other mechanical, thermal and optical changes are less well studied but offer the opportunity to gather independent information about the molecular changes at the basis of the excitation (Cohen, 1973;Watanabe, 1986).…”