Abstract.
Ion channel expression was studied in THP-1 human monocytic leukemia cells induced to differentiate into macrophage-like cells by exposure to the phorbol ester, phorbol 12-myristate 13-acetate (PMA). Inactivating delayed rectifier K+ currents, I DR, present in almost all undifferentiated THP-1 monocytes, were absent from PMA-differentiated macrophages. Two K+ channels were observed in THP-1 cells only after differentiation into macrophages, an inwardly rectifying K+ channel (I IR) and a Ca2+-activated maxi-K channel (I BK). I IR was a classical inward rectifier, conducting large inward currents negative to E K and very small outward currents. I IR was blocked in a voltage-dependent manner by Cs+, Na+, and Ba2+, block increasing with hyperpolarization. Block by Na+ and Ba2+ was time-dependent, whereas Cs+ block was too fast to resolve. Rb+ was sparingly permeant. In cell-attached patches with high [K+] in the pipette, the single I IR channel conductance was ∼30 pS and no outward current could be detected. I BK channels were observed in cell-attached or inside-out patches and in whole-cell configuration. In cell-attached patches the conductance was ∼200–250 pS and at potentials positive to ∼100 mV a negative slope conductance of the unitary current was observed, suggesting block by intracellular Na+. I BK was activated at large positive potentials in cell-attached patches; in inside-out patches the voltage-activation relationship was shifted to more negative potentials by increased [Ca2+]. Macroscopic I BK was blocked by external TEA+ with half block at 0.35 mm. THP-1 cells were found to contain mRNA for Kv1.3 and IRK1. Levels of mRNA coding for these K+ channels were studied by competitive PCR (polymerase chain reaction), and were found to change upon differentiation in the same direction as did channel expression: IRK1 mRNA increased at least 5-fold, and Kv1.3 mRNA decreased on average 7-fold. Possible functional correlates of the changes in ion channel expression during differentiation of THP-1 cells are discussed.
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Received: 19 September 1995/Revised: 14 March 1996
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DeCoursey, T., Kim, S., Silver, M. et al. III. Ion Channel Expression in PMA-differentiated Human THP-1 Macrophages. J. Membrane Biol. 152, 141–157 (1996). https://doi.org/10.1007/s002329900093
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DOI: https://doi.org/10.1007/s002329900093