Enhancement of Voltage-gated Na+ Channel Current Associated with Multidrug Resistance in Human Leukemia Cells1

Membrane currents were examined in a drug-sensitive human leukemia cell line (K562) and its multidrug-resistant cell line (K562/ADM) under the whole-cell variation of the patch electrode voltage clamp technique. Most K562 cells showed only the outward current, which was completely suppressed by internal Cs* ions and 20 HIMethyleneglycol bis(0-aminoethyl ctht-r)-.V..V..V. V'-tetraacelkacid. In contrast to K562 cells, most K562/ADM cells showed tetrodotoxin-sensitive, voltage-gated Na* chan nel current in addition to the outward current. Na* current was observed in four of 29 K562 cells examined, while it was observed in 29 of 33 K562/ADM cells. Two revenant cell lines (Rl-3, Rl-5) did not show Na* current. It was concluded that the amplitude of voltage-gated \V current increases in association with multidrug resistance in human leukemia cells.