VOLTAGE-DEPENDENT CATIONIC CHANNEL OF ESCHERICHIA-COLI

A fraction highly enriched with inner membranes of E. coli was fused w ith liposomes, using the dehydration-rehydration technique, to produce giant liposomes amenable to patch-clamp recordings. Among the several channels present in this type of preparation, one was further charact erized. The channel has a conductance of some 200 pS (in 0.1 M KCl) an d is weakly selective for cations (PK/PCl = 4). The channel stays open at negative and low positive membrane potentials and shows an increas ing probability of closure with increasing voltage. High positive memb rane potentials favor transitions to a long-lived inactivated state. f ollowing slow kinetics. Voltage-dependent rapid flickerings of the sam e amplitude, between open state and other short-lived closed states, a re superposed on these kinetics. The channel is presumed to be localiz ed in the inner membrane, but its characteristics are also compatible with those of porins of the outer membrane. However, the major porins OmpF and OmpC, purified and reconstituted into giant liposomes, exhibi ted a marked different behavior.