Elevation of a potassium current in differentiating human leukemic (HL‐60) cells

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Abstract
Human promyelocytic leukemia (HL‐60) cells display a novel voltage‐dependent outward current under voltage clamp. This current is present at low levels in the proliferative state and in granulocytes derived from HL‐60 cells which were induced to differentiate with retinoic acid. It is elevated in macrophages derived from HL‐60 cells after exposure to phorbol‐12‐myristate‐13‐acetate (PMA). The current is carried primarily by K+, is blocked by Cs+ and by increased intracellular concentrations of Cl−. From a holding potential of −80 mV, significant activation required depolarization to +20 mV membrane potential. Activation was not influenced by intracellular Ca2+ (1–2 × 10−6M). These properties appear to differ significantly from the Ca2+‐activated K+ channel and the delayed rectifier. The increase of this voltage‐activated current in differentiation toward the macrophage, but not the granulocyte, suggests that this current is correlated specifically with macrophage differentiation.