title: Ion channel expression in PMA-differentiated human THP-1 macrophages.
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, IDR, 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 (IIR) and a Ca2+-activated maxi-K channel (IBK). IIR was a classical inward rectifier, conducting large inward currents negative to EK and very small outward currents. IIR 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 IIR channel conductance was approximately 30 pS and no outward current could be detected. IBK channels were observed in cell-attached or inside-out patches and in whole-cell configuration. In cell-attached patches the conductance was approximately 200-250 pS and at potentials positive to approximately 100 mV a negative slope conductance of the unitary current was observed, suggesting block by intracellular Na+. IBK 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 IBK 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.
authors.affiliation: Department of Molecular Biophysics and Physiology, Rush Presbyterian St. Luke's Medical Center, 1653 West Congress Parkway Chicago, IL 60612, USA.
authors.forename: T E
authors.initials: TE
authors.lastname: DeCoursey
authors.forename: S Y
authors.initials: SY
authors.lastname: Kim
authors.forename: M R
authors.initials: MR
authors.lastname: Silver
authors.forename: F N
authors.initials: FN
authors.lastname: Quandt
mesh_terms: D001483:Base Sequence; D002413:Cations, Divalent / Q000494:pharmacology; D002454:Cell Differentiation / Q000187:drug effects; D015972:Gene Expression Regulation, Neoplastic / Q000187:drug effects*; D006801:Humans; D015640:Ion Channel Gating / Q000187:drug effects; D007473:Ion Channels / Q000096:biosynthesis* / Q000235:genetics; D051664:Kv1.3 Potassium Channel; D051036:Large-Conductance Calcium-Activated Potassium Channels; D008264:Macrophages / Q000187:drug effects / Q000378:metabolism*; D008969:Molecular Sequence Data; D009000:Monocytes / Q000502:physiology*; D009363:Neoplasm Proteins / Q000096:biosynthesis* / Q000235:genetics; D018408:Patch-Clamp Techniques; D016133:Polymerase Chain Reaction; D015221:Potassium Channels / Q000187:drug effects / Q000378:metabolism; D024681:Potassium Channels, Calcium-Activated; D024661:Potassium Channels, Inwardly Rectifying; D024642:Potassium Channels, Voltage-Gated; D011522:Protons; D012333:RNA, Messenger / Q000096:biosynthesis; D012334:RNA, Neoplasm / Q000096:biosynthesis; D012689:Sequence Homology, Nucleic Acid; D013045:Species Specificity; D013755:Tetradecanoylphorbol Acetate / Q000494:pharmacology*; D019789:Tetraethylammonium; D013757:Tetraethylammonium Compounds / Q000494:pharmacology
chemical_list: D002413:Cations, Divalent; D007473:Ion Channels; C496973:KCNA3 protein, human; D051664:Kv1.3 Potassium Channel; D051036:Large-Conductance Calcium-Activated Potassium Channels; D009363:Neoplasm Proteins; D015221:Potassium Channels; D024681:Potassium Channels, Calcium-Activated; D024661:Potassium Channels, Inwardly Rectifying; D024642:Potassium Channels, Voltage-Gated; D011522:Protons; D012333:RNA, Messenger; D012334:RNA, Neoplasm; D013757:Tetraethylammonium Compounds; D019789:Tetraethylammonium; D013755:Tetradecanoylphorbol Acetate