In vitro demonstration of sodium channels in nervous tissues

Abstract

The membrane fraction isolated from cattle brain and vagal nerve were treated by ultrasound irradiation is the presence of 22Na. Sonicated membranes were separated from the radioactive solution by gel chromatography on Sephadex G-25. It was shown that the quantity of 22Na bound to Sonicated membranes was ten times higher when a radioactive label was present in the medium during sonication as compared with the experiments where 22Na was added immediately after sonication. 22Na associated with Sonicated membranes was trapped in an osmotically active form and slowly released into a non-radioactive solution. It is suggested that the membrane fragments after brief sonication make closed vesicles which immobilize solutes of the environment. The efflux of 22Na from vesicles was studied in the presence and in the absence of substances which change the sodium conductance of excitable membranes. The local anaesthetics (procaine, dibucaine) and tetrodotoxin at concentrations which block electrical excitation in vivo decreased the 22Na efflux from the vesicles. Veratrine, an activator of sodium channels, increased this efflux. The results are interpreted as an indication of the presence of functionally active sodium channels in the isolated membrane fragments. We suggest that such vesicles could be used also for the identification of the ion-selective channels in nerve membranes.