The Kv channel blocker 4-aminopyridine enhances Ag+ uptake: a scanning electrochemical microscopy study of single living cells

We report that silver ion (Ag⁺) uptake is enhanced by 4-aminopyridine (4-AP), a well known voltage-sensitive potassium ion channel (K_v) blocker. Both bacterial (Escherichia coli) and mammalian (3T3 fibroblast) cells were used as model systems. Ag⁺ uptake was monitored with a scanning electrochemical microscope with an amperometric Ag⁺ ion-selective electrode (Ag⁺-ISE) and the respiration rates of E. coli cells were measured by oxygen reduction at an ultramicroelectrode. The results showed that not only the amount but also the rate of silver uptake by the cells increased significantly when 4-AP was added to the solution. For fibroblasts, the Ag⁺ uptake rate was 4.8 × 10⁷ ions per cell per sec without 4-AP compared with 1.0 × 10⁸ ions per cell per sec with 0.2 mM 4-AP. For E. coli cells, the uptake rate was 1.5 × 10⁴ ions per cell per sec without 4-AP vs. 3.5 × 10⁴ ions per cell per sec with 0.5 mM 4-AP and 5.9 × 10⁴ ions per cell per sec with 1 mM 4-AP. Thus, 4-AP might be useful where silver is used as antimicrobial agent to speed its uptake.