title: Facilitation of Ca2+-activated K+ channels (IKCa1) by mibefradil in B lymphocytes.
abstract: K+ channels play critical roles in the proliferation and activation of lymphocytes. Mouse B cells express large-conductance background K+ channel (LK bg) in addition to the voltage-gated K+ channel (Kv) and Ca2+-activated K+ channel current (IKCa1). Mibefradil, a blocker of T-type Ca2+ channels, has been reported to affect the proliferation of immune cells. In this study, we investigated the effects of mibefradil on the membrane potential and ion channels in murine B cell lines, WEHI-231 and Bal-17. In the whole-cell patch clamp experiments, mibefradil blocked Kv and LK bg current with half inhibitory concentration (IC50), 1.9 and 2.3 microM, respectively. Interestingly, IKCa1 current was increased by mibefradil. In the inside-out patch clamp study with cloned murine IKCa1 (mIKCa1) in HEK-293, mibefradil increased both Ca2+ sensitivity and maximum activity of mIKCa1. At high concentrations (>10 microM), mibefradil inhibited mIKCa1 in a voltage-dependent manner. Application of anti-IgM antibody to stimulate B cell receptors (BCR-ligation) induced transient hyperpolarization of Bal-17 and WEHI-231 cells, which became persistent with 1 microM mibefradil. The hyperpolarizing response was abolished by charybdotoxin, a selective blocker for SK4/IKCa1. In summary, our study firstly reports the ion channel-activating effects of mibefradil. The selective potent activation of IKCa1 suggests that mibefradil-derived drugs might be useful in the control of cell responses related with IKCa1.
authors.affiliation: Department of Physiology, Seoul National University College of Medicine, Seoul, South Korea.
authors.forename: Hae Young
authors.initials: HY
authors.lastname: Yoo
authors.forename: Haifeng
authors.initials: H
authors.lastname: Zheng
authors.forename: Joo Hyun
authors.initials: JH
authors.lastname: Nam
authors.forename: Yen Hoang
authors.initials: YH
authors.lastname: Nguyen
authors.forename: Tong Mook
authors.initials: TM
authors.lastname: Kang
authors.forename: Yung E
authors.initials: YE
authors.lastname: Earm
authors.forename: Sung Joon
authors.initials: SJ
authors.lastname: Kim
mesh_terms: D000818:Animals; D001402:B-Lymphocytes / Q000187:drug effects* / Q000378:metabolism; D002118:Calcium / Q000378:metabolism; D002121:Calcium Channel Blockers / Q000494:pharmacology; D002460:Cell Line; D018999:Charybdotoxin / Q000494:pharmacology; D004305:Dose-Response Relationship, Drug; D006801:Humans; D051660:Intermediate-Conductance Calcium-Activated Potassium Channels / Q000819:agonists* / Q000235:genetics / Q000378:metabolism; D008213:Lymphocyte Activation / Q000187:drug effects*; D008564:Membrane Potentials; D049990:Membrane Transport Modulators / Q000494:pharmacology*; D020748:Mibefradil / Q000494:pharmacology*; D051379:Mice; D018408:Patch-Clamp Techniques; D026902:Potassium Channel Blockers / Q000494:pharmacology; D024642:Potassium Channels, Voltage-Gated / Q000037:antagonists & inhibitors / Q000378:metabolism; D014162:Transfection
chemical_list: D002121:Calcium Channel Blockers; D051660:Intermediate-Conductance Calcium-Activated Potassium Channels; C496925:Kcnn4 protein, mouse; D049990:Membrane Transport Modulators; D026902:Potassium Channel Blockers; D024642:Potassium Channels, Voltage-Gated; D018999:Charybdotoxin; D020748:Mibefradil; D002118:Calcium