title: Constitutive expression of a Mg2+-inhibited K+ current and a TRPM7-like current in human erythroleukemia cells.
abstract: Whole cell patch-clamp experiments were undertaken to define the basal K(+) conductance(s) in human erythroleukemia cells and its contribution to the setting of resting membrane potential. Experiments revealed a non-voltage-activated, noninactivating K(+) current. The magnitude of the current recorded under whole cell conditions was inhibited by an increase in free intracellular Mg(2+) concentration. Activation or inactivation of the Mg(2+)-inhibited K(+) current (MIP) was paralleled by activation or inactivation of a Mg(2+)-inhibited TRPM7-like current displaying characteristics indistinguishable from those reported for molecularly identified TRPM7 current. The MIP and TRPM7 currents were inhibited by 5-lipoxygenase inhibitors. However, inhibition of the MIP current was temporally distinct from inhibition of TRPM7 current, allowing for isolation of the MIP current. Isolation of the MIP conductance revealed a current reversing near the K(+) equilibrium potential, indicative of a highly K(+)-selective conductance. Consistent with this finding, coactivation of the nonselective cation current TRPM7 and the MIP current following dialysis with nominally Mg(2+)-free pipette solution resulted in hyperpolarized whole cell reversal potentials, consistent with an important role for the MIP current in the setting of a negative resting membrane potential. The MIP and TRPM7-like conductances were constitutively expressed under in vivo conditions of intracellular Mg(2+), as judged by their initial detection and subsequent inactivation following dialysis with a pipette solution containing 5 mM free Mg(2+). The MIP current was blocked in a voltage-dependent fashion by extracellular Cs(+) and, to a lesser degree, by Ba(2+) and was blocked by extracellular La(3+) and 2-aminoethoxydiphenyl borate. MIP currents were unaffected by blockers of ATP-sensitive K(+) channels, human ether-à-go-go-related gene current, and intermediate-conductance Ca(2+)-activated K(+) channels. In addition, the MIP current displayed characteristics distinct from conventional inwardly rectifying K(+) channels. A similar current was detected in the leukemic cell line CHRF-288-11, consistent with this current being more generally expressed in cells of leukemic origin.
authors.affiliation: Department of Physiology, Development, and Neuroscience, University of Cambridge, UK. mjm39@cam.ac.uk
authors.forename: Michael J
authors.initials: MJ
authors.lastname: Mason
authors.forename: Catherine
authors.initials: C
authors.lastname: Schaffner
authors.forename: R Andres
authors.initials: RA
authors.lastname: Floto
authors.forename: Quok An
authors.initials: QA
authors.lastname: Teo
mesh_terms: D002412:Cations / Q000378:metabolism; D004553:Electric Conductivity; D006801:Humans; D004915:Leukemia, Erythroblastic, Acute / Q000378:metabolism* / Q000473:pathology; D016859:Lipoxygenase Inhibitors / Q000494:pharmacology; D008274:Magnesium / Q000378:metabolism*; D008564:Membrane Potentials / Q000502:physiology; D018408:Patch-Clamp Techniques; D011188:Potassium / Q000378:metabolism*; D015221:Potassium Channels / Q000502:physiology*; D017346:Protein Serine-Threonine Kinases; D050053:TRPM Cation Channels / Q000037:antagonists & inhibitors / Q000378:metabolism*; D014407:Tumor Cells, Cultured
chemical_list: D002412:Cations; D016859:Lipoxygenase Inhibitors; D015221:Potassium Channels; D050053:TRPM Cation Channels; D017346:Protein Serine-Threonine Kinases; C486583:TRPM7 protein, human; D008274:Magnesium; D011188:Potassium