MECHANISM OF BLOCKAGE OF AMPHOTERICIN-B CHANNELS IN A LIPID BILAYER

Some organic compounds (non-electrolytes, tetraalkylammonia, etc.) with a molecular size of 6-8 .ANG. decrease the conductance of ionic channels formed in the lipid bilayer by a polyene antibiotic amphotericin B. Upon entering the channel these compounds apparently block the passage of inorganic ions. The extent of conductance blockage by organic ions depends on the membrane potential and electrolyte concentration. In the presence of ionic blockers, e.g., tetraethylammonium, amphotericin B-containing membranes assume some properties characteristic of excitable membranes (i.e., the current-voltage characteristic acquires the negative resistance region) and in response to a potential step, activation followed by inactivation of conductance is observed. The potential dependence of the blockage is due to interaction inside the channel of the blocker ion with penetrating ions, by a mechanism similar to that described by Armstrong for blockage of squid axon K+ channels by ammonium derivatives.