Ion selectivity of the nerve membrane sodium channel incorporated into liposomes

Abstract

Tetrodotoxin-sensitive sodium channels of lobster nerve membranes were incorporated into soybean liposomes by the freeze-thaw-sonication procedure and their ionic selectivity was studied. Veratridine and grayanotoxin-I were used to activate the sodium channels and the increment of the ionic flux through them was specifically abolished by tetrodotoxin. The drug-sensitive 22Na +, 42K +, 86Rb + and 137Cs + influxes were measured. The permeability ratios calculated directly from ion fluxes showed that the channels preferably allow the passage of Na +. No anion influx ([ 32P]phosphate, [ 35S]sulfate, 36Cl) sensitive to the drugs was observed. The data reveal that the sodium channels incorporated into liposomes remain cation-selective and discriminate among different cations.