Influence of cepharanthin and hyperthermia on the intracellular accumulation of adriamycin and Fluo3, an indicator of Ca²⁺

In the present study, the mechanism involved in the enhancement of adriamycin (ADR) accumulation by cepharanthin (CEP) and hyperthermia were examined. The accumulation of ADR and Fluo3 (an indicator of Ca²⁺) was increased by treatment with CEP. This suggests that ADR accumulation may increase due to increased influx of Ca²⁺. The ADR accumulation increased with increasing the KCl concentration in the presence of CEP when the KCl concentation was over 200 mM. This demonstrates that ADR accumulation increases with treatment with CEP and increasing the KCl concentration after the cell membrane potential reaches 0. ADR accumulation did not change with the extracellular pH in the absence of NaHCO₃. CEP increased the ADR accumulation with increasing extracellular pH, regardless of NaHCO₃. This suggests that CEP may affect the H+ flux, and consequently increase ADR accumulation regardless of NaHCO₃. Further, it increased with increasing extracellular pH in the presence of NaHCO₃, regardless of CEP. It is thought that the interaction between H+ and HCO_3- may cause increased ADR accumulation. ADR accumulation was decreased by DIDS and amiloride at 37°C. ADR accumulation in the presence of amiloride at 45°C was increased compared with that at 37°C. However, the accumulation combined with amiloride and hyperthermia was lower than with treatment with ADR only at 37°C. This indicates that ADR accumulation is decreasd by amiloride and increased by hyperthermia. ADR accumulation is further decreased by DIDS at 45°C compared with 37°C. This suggests that the H+ flux in hyperthermia is influenced by Cl/HCO_3- exchanger but not Na+/H+ exchanger.