title: Distinct metal ion binding sites on Ca(2+)-activated K+ channels in inside-out patches of human erythrocytes.
abstract: Effects of Cd2+, Co2+, Pb2+, Fe2+ and Mg2+ (1-100 microM) on single-channel properties of the intermediate conductance Ca(2+)-activated K+ (CaK) channels were investigated in inside-out patches of human erythrocytes in a physiological K+ gradient. Cd2+, Co2+ and Pb2+, but not Fe2+ and Mg2+, were able to induce CaK channel openings. The potency of the metals to open CaK channels in human erythrocytes follows the sequence Pb2+, Cd2+ > Ca2+ > or = Co2+ >> Mg2+, Fe2+. At higher concentrations Pb2+, Cd2+ and Co2+ block the CaK channel by reducing the opening frequency and the single-channel current amplitude. The potency of the metals to reduce CaK channel opening frequency follows the sequence Pb2+ > Cd2+, Co2+ >> Ca2+, which differs from the potency sequence Cd2+ > Pb2+, Co2+ >> Ca2+ to reduce the unitary single-channel current amplitude. Fe2+ reduced the channel opening frequency and enhanced the two open times of CaK channels activated by Ca2+, whereas up to 100 microM Mg2+ had no effect on any of the measured single-channel parameters. It is concluded that the activation of CaK channels of human erythrocytes by various metal ions occurs through an interaction with the same regulatory site at which Ca2+ activates these channels. The different potency orders for the activating and blocking effects suggest the presence of at least one activation and two blocking sites. A modulatory binding site for Fe2+ exists as well. In addition, the CaK channels in human erythrocytes are distinct from other subtypes of Ca(2+)-activated K+ channels in their sensitivity to the metal ions.
authors.affiliation: Research Institute of Toxicology, University of Utrecht, Netherlands.
authors.forename: T
authors.initials: T
authors.lastname: Leinders
authors.forename: R G
authors.initials: RG
authors.lastname: van Kleef
authors.forename: H P
authors.initials: HP
authors.lastname: Vijverberg
mesh_terms: D001665:Binding Sites; D002118:Calcium / Q000378:metabolism*; D002413:Cations, Divalent; D004910:Erythrocyte Membrane / Q000378:metabolism* / Q000502:physiology; D006801:Humans; D008564:Membrane Potentials; D008670:Metals / Q000378:metabolism*; D015221:Potassium Channels / Q000378:metabolism*
chemical_list: D002413:Cations, Divalent; D008670:Metals; D015221:Potassium Channels; D002118:Calcium