Influence of cell membrane potential, and selectivity of the Na⁺/H⁺ exchanger and Cl^-/HCO₃^- exchanger on the intracellular accumulation of adriamycin

Intracellular accumulation of adriamycin (ADR) has been reported to be influenced by cell membrane potential. We first evaluated intracellular accumulation of ADR and 3,3′-(di-n-hexyl)-2,2′-oxacarbocyanine iodide (NK-2280), an indicator of cell membrane potential, and found a good correlation between ADR and NK-2280 intracellular accumulation in several cell lines. This suggests that ADR accumulation may be influenced by cell membrane potential or the mechanisms of NK-2280 accumulation may be similar to those of ADR accumulation. Next, we observed the influence of the Na⁺ /H⁺ exchanger and Cl^-/HCO₃^- exchanger on the intracellular accumulation of ADR and NK-2280, and found that ADR accumulation decreased with increasing concentratios of 3,5-diamino-6-chloro-N-(diaminomethylene)pyrazinecarboxamide (amiloride), an inhibitor of the Na⁺ /H⁺ exchanger, and 4,4′-diisothiocyanato-stilbene-2,2′-disulfonic acid (DIDS), an inhibitor of the Cl^- /HCO₃^- exchanger, however, NK-2280 accumulation was increased by amiloride, and decreased by DIDS. The increased accumulation of NK-2280 induced by amiloride may be due to the increased cell membrane potential caused by the inhibition of H⁺ ion efflux and Na⁺ ion influx due to the inhibition of the Na⁺/H⁺ exchanger. The decreased accumulation of NK-2280 may be also due to the decreased cell membrane potential caused by the inhibition of Cl^- ion efflux due to the inhibition of the Cl^-/HCO₃^- exchanger by DIDS. However, the decreased rate caused by DIDS was greater than the increased rate caused by amiloride. Therefore, it is suggested that the decreased accumulation of NK-2280 by DIDS may be influenced by other factors apart from cell membrane potential. These results suggest that the Cl^-/HCO₃^- exchanger may be related to both ADR accumulation, and NK-2280 accumulation, and that the Na⁺ /H⁺ exchanger may be related to ADR accumulation, but not NK-2280. This suggests that the Cl^-/HCO₃^- exchanger is of low selectivity.