Proton/sodium ion antiport in Escherichia coli

In anaerobic suspensions of Escherichia coli, after H(+) ions have been translocated outwards across the plasma membrane by a respiratory pulse, re-equilibration is catalysed by Na(+). The sudden addition of a Na(+) salt causes the effective outward translocation of H(+) by an electroneutral process. We conclude that the plasma membrane of E. coli contains a Na(+)/H(+) antiport system that normally translocates Na(+) outwards under the influence of an inwardly directed H(+)-activity gradient.