Pressure Effect on the Membrane Action of a Nerve-Blocking Spin Label

A reversible nerve-blocking spin label, 2,2,6,6-tetramethylpiperidine-1-oxyl (TEMPO) was used to study the nature of anesthetic-binding sites in nerve membranes as a function of pressure. The nerve-blocking effect of TEMPO is enhanced under pressure. At atmospheric pressure, TEMPO blocks nerve conduction by solubilizing in the apolar region of the nerve membrane. However, the nerve-conduction-block by TEMPO at 150 atm of helium was related to the binding of TEMPO to a pressure-induced high-affinity polar site in the nerve membrane. The new TEMPO-binding site could not be detected in lipid model membranes and, thus, the involvement of membrane protein in the new site was inferred. Pressure may induce a nerve membrane conformation change in the presence of TEMPO. The observation that under different pressure, a single anesthetic, i.e., TEMPO, was capable of blocking nerve conduction by binding to two different sites within the nerve membrane, supports the view that there are multiple anesthetic receptor sites, which differ in chemical composition and location within the nerve membrane. These sites, when occupied by different classes of anesthetics, produce the general phenomenon of nerve-conduction block. The enhancement of nerve-conduction block by pressure may be due to the increased concentration of TEMPO in the new site in the nerve membrane under pressure.