title: Properties of Mg(2+)-dependent cation channels in human leukemia K562 cells.
abstract: The endogenous Mg(2+)-inhibited cation (MIC) current was recently described in different cells of hematopoietic lineage and was implicated in the regulation of Mg2+ homeostasis. Here we present a single channel study of endogenously expressed Mg(2+)-dependent cation channels in the human myeloid leukemia K562 cells. Inwardly directed unitary currents were activated in cell-attached experiments in the absence of Ca2+ and Mg2+ in the pipette solution. The current-voltage (I-V) relationships displayed strong inward rectification and yielded a single channel slope conductance of approximately 30 pS at negative potentials. The I-V relationships were not altered by patch excision into divalent-free solution. Channel open probability (P(o)) and mean closed time constant (tau(C)) were strongly voltage-dependent, indicating that gating mechanisms may underlie current inward rectification. Millimolar concentrations of Ca2+ or Mg2+ applied to the cytoplasmic side of the membrane produced slow irreversible inhibition of channel activity. The Mg(2+)-dependent cation channels described in this study differ from the MIC channels described in human T-cells, Jurkat, and rat basophilic leukemia (RBL) cells in their I-V relationships, kinetic parameters and dependence on intracellular divalent cations. Our results suggested that endogenously expressed Mg(2+)-dependent cation channels in K562 cells and the MIC channels in other hematopoietic cells might be formed by different channel proteins.
authors.affiliation: Institute of Cytology RAS, 4 Tikhoretsky Ave., St. Petersburg, Russia.
authors.forename: Svetlana B
authors.initials: SB
authors.lastname: Semenova
authors.forename: Alla F
authors.initials: AF
authors.lastname: Fomina
authors.forename: Irina O
authors.initials: IO
authors.lastname: Vassilieva
authors.forename: Yuri A
authors.initials: YA
authors.lastname: Negulyaev
mesh_terms: D002118:Calcium / Q000008:administration & dosage / Q000494:pharmacology; D015220:Calcium Channels / Q000235:genetics; D002412:Cations / Q000378:metabolism*; D045744:Cell Line, Tumor; D002462:Cell Membrane / Q000187:drug effects; D003593:Cytoplasm / Q000187:drug effects; D004305:Dose-Response Relationship, Drug; D004553:Electric Conductivity; D006801:Humans; D007473:Ion Channels / Q000037:antagonists & inhibitors / Q000378:metabolism*; D007951:Leukemia, Myeloid / Q000378:metabolism* / Q000473:pathology / Q000503:physiopathology; D008274:Magnesium / Q000008:administration & dosage / Q000378:metabolism* / Q000494:pharmacology; D018408:Patch-Clamp Techniques; D012333:RNA, Messenger / Q000378:metabolism; D020133:Reverse Transcriptase Polymerase Chain Reaction; D050916:TRPV Cation Channels / Q000235:genetics
chemical_list: D015220:Calcium Channels; D002412:Cations; D007473:Ion Channels; D012333:RNA, Messenger; D050916:TRPV Cation Channels; C422827:TRPV6 protein, human; D008274:Magnesium; D002118:Calcium