Inducing and Reversing Anesthesia with Temperature Variation - Experiments on an Excised Frog Sciatic Nerve

Abstract

The Meyer-Overton Rule and other more recent experimental observations suggest that the fluidity of the lipid membrane is involved in nerve propagation and in mechanisms behind anesthesia. In other words, Hodgkin-Huxley may not be telling the whole story. Under physiological conditions a cell membrane operates very close to the melting transition, i.e., to the point where the fluid membrane becomes a solid gel. Recent theoretical work indicates that signal propagation in a nerve cell may also involve a thermo-acoustic pulse of partial gellification. Natural selection should have led to optimal propagation under physiological conditions.When apolar molecules are dissolved in the apolar membrane of the nerve cell, the freezing temperature of the membrane is lowered. This would interfere with pulse propagation and thus lead to anesthesia. However, if the theory is right, the effect should be reversed if we let the propagation take place at lower temperature. This is because the lower temperature would bring us closer again to the freezing transition.We experimentally test this idea on the sciatic nerve of frogs. We follow the propagation of a signal with different concentrations of Argon in the medium and at different temperatures. Argon is an anesthetic that is chemically inert and it is expected to have its anesthetic effect just through interfering with the fluidity of the membrane. As a control we also perform the same experiments with Lidocain as the involved anesthetic. Lidocain is an anesthetic that is well known to work through interfering with voltage gated sodium channels.