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 NaHC03 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.