title: Activation of calcium- and voltage-gated potassium channels of large conductance by leukotriene B4.
abstract: Calcium/voltage-gated, large conductance potassium (BK) channels control numerous physiological processes, including myogenic tone. BK channel regulation by direct interaction between lipid and channel protein sites has received increasing attention. Leukotrienes (LTA4, LTB4, LTC4, LTD4, and LTE4) are inflammatory lipid mediators. We performed patch clamp studies in Xenopus oocytes that co-expressed BK channel-forming (cbv1) and accessory β1 subunits cloned from rat cerebral artery myocytes. Leukotrienes were applied at 0.1 nm-10 μm to either leaflet of cell-free membranes at a wide range of [Ca(2+)]i and voltages. Only LTB4 reversibly increased BK steady-state activity (EC50 = 1 nm; Emax reached at 10 nm), with physiological [Ca(2+)]i and voltages favoring this activation. Homomeric cbv1 or cbv1-β2 channels were LTB4-resistant. Computational modeling predicted that LTB4 docked onto the cholane steroid-sensing site in the BK β1 transmembrane domain 2 (TM2). Co-application of LTB4 and cholane steroid did not further increase LTB4-induced activation. LTB4 failed to activate β1 subunit-containing channels when β1 carried T169A, A176S, or K179I within the docking site. Co-application of LTB4 with LTA4, LTC4, LTD4, or LTE4 suppressed LTB4-induced activation. Inactive leukotrienes docked onto a portion of the site, probably preventing tight docking of LTB4. In summary, we document the ability of two endogenous lipids from different chemical families to share their site of action on a channel accessory subunit. Thus, cross-talk between leukotrienes and cholane steroids might converge on regulation of smooth muscle contractility via BK β1. Moreover, the identification of LTB4 as a highly potent ligand for BK channels is critical for the future development of β1-specific BK channel activators.
authors.affiliation: From the Department of Pharmacology, University of Tennessee Health Science Center, Memphis, Tennessee 38163 and abukiya@uthsc.edu.
authors.forename: Anna N
authors.initials: AN
authors.lastname: Bukiya
authors.affiliation: the Department of Chemistry and Computational Research on Materials Institute (CROMIUM), University of Memphis, Memphis, Tennessee 38152.
authors.forename: Jacob
authors.initials: J
authors.lastname: McMillan
authors.affiliation: From the Department of Pharmacology, University of Tennessee Health Science Center, Memphis, Tennessee 38163 and.
authors.forename: Jianxi
authors.initials: J
authors.lastname: Liu
authors.affiliation: From the Department of Pharmacology, University of Tennessee Health Science Center, Memphis, Tennessee 38163 and.
authors.forename: Bangalore
authors.initials: B
authors.lastname: Shivakumar
authors.affiliation: the Department of Chemistry and Computational Research on Materials Institute (CROMIUM), University of Memphis, Memphis, Tennessee 38152.
authors.forename: Abby L
authors.initials: AL
authors.lastname: Parrill
authors.affiliation: From the Department of Pharmacology, University of Tennessee Health Science Center, Memphis, Tennessee 38163 and adopico@uthsc.edu.
authors.forename: Alex M
authors.initials: AM
authors.lastname: Dopico
mesh_terms: D000818:Animals; D002118:Calcium / Q000378:metabolism; D002536:Cerebral Arteries / Q000166:cytology; D005260:Female; D015640:Ion Channel Gating / Q000187:drug effects / Q000235:genetics / Q000502:physiology*; D051037:Large-Conductance Calcium-Activated Potassium Channel alpha Subunits / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D051038:Large-Conductance Calcium-Activated Potassium Channel beta Subunits / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D017572:Leukotriene A4 / Q000737:chemistry / Q000378:metabolism / Q000494:pharmacology; D007975:Leukotriene B4 / Q000737:chemistry / Q000378:metabolism* / Q000494:pharmacology; D017997:Leukotriene C4 / Q000737:chemistry / Q000378:metabolism / Q000494:pharmacology; D017998:Leukotriene D4 / Q000737:chemistry / Q000378:metabolism / Q000494:pharmacology; D017999:Leukotriene E4 / Q000737:chemistry / Q000378:metabolism / Q000494:pharmacology; D008564:Membrane Potentials / Q000187:drug effects; D008845:Microinjections; D008958:Models, Molecular; D015394:Molecular Structure; D032342:Muscle Cells / Q000166:cytology / Q000378:metabolism; D009865:Oocytes / Q000187:drug effects / Q000378:metabolism / Q000502:physiology; D018408:Patch-Clamp Techniques; D011485:Protein Binding; D017434:Protein Structure, Tertiary; D018075:RNA, Complementary / Q000008:administration & dosage / Q000235:genetics; D051381:Rats; D014982:Xenopus laevis
chemical_list: C545899:KCNMB1 protein, rat; C494842:Kcnma1 protein, rat; D051037:Large-Conductance Calcium-Activated Potassium Channel alpha Subunits; D051038:Large-Conductance Calcium-Activated Potassium Channel beta Subunits; D017572:Leukotriene A4; D018075:RNA, Complementary; D007975:Leukotriene B4; D017997:Leukotriene C4; D017998:Leukotriene D4; D017999:Leukotriene E4; D002118:Calcium
keywords: Computer Modeling; Drug Design; Ion Channel; Leukotriene; Patch Clamp