Influence of extracellular ion concentration on the intracellular accumulation of adriamycin

The cytotoxic action of adriamycin is influenced by its intracellular accumulation. Therefore, it is important to clarify the mechanisms of adriamycin influx and efflux. In the present study, the influence of the extracellular KCl and Ca²⁺ concentration, the extracellular pH and the presence of NaHCO₃ on the ADR accumulation was investigated in order to study the mechanisms in ADR accumulation influenced by ions. The extracellular KCl concentration did not affect the intracellular ADR accumulation. This suggests the cell membrane potential does not affect the ADR accumulation since it is influenced by the KCl concentration. The intracellular intensity of fluorescence of Fluo3, an indicator of Ca²⁺, increased between 0 and 20 mM of the extracellular concentration of Ca²⁺ ion. However, the ADR accumulation did not change between 0 and 20 mM of the extracellular concentration of Ca²⁺. This indicates that the extracellular concentration of Ca²⁺ does not affect the ADR accumulation under physiological conditions since 20 mM of Ca²⁺ is beyond normal physiological conditions. Further, the intracellular fluorescence of Fluo3 decreased as increasing the extracellular pH. In contrast, the ADR accumulation increased as increasing the extracellular pH. These suggest that the ADR accumulation increases as decreasing the intracellular Ca²⁺ as changing the extracellular pH- In wild type strain, the ADR accumulation did not change by the extracellular pH in the absence of NaHCO₃, but increased as increasing the extracellular pH in the presence of NaHCO₃. This suggests that the ADR accumulation in the wild type strain is influenced by NaHCO₃ but the extracellular pH. In the ADR-resistant strain, the ADR accumulation decreased as increasing the extracellular pH regardless of NaHCO₃. However, the accumulation of ADR increased as increasing the extracellular pH when the adjustment of pH was carried out with 1N HCl. This suggests that Cl^- may play an important role in the ADR influx in the ADR-resistant strain.