title: Dynamic coupling between TRPV4 and Ca2+-activated SK1/3 and IK1 K+channels plays a critical role in regulating the K+-secretory BK channel in kidney collecting duct cells.
abstract: The large-conductance Ca2+-activated K+channel, BK (KCNMA1), is expressed along the connecting tubule (CNT) and cortical collecting duct (CCD) where it underlies flow- and Ca2+-dependent K+secretion. Its activity is partially under the control of the mechanosensitive transient receptor potential vanilloid type 4 (TRPV4) Ca2+-permeable channel. Recently, we identified three small-/intermediate-conductance Ca2+-activated K+channels, SK1 (KCNN1), SK3 (KCNN3), and IK1 (KCNN4), with notably high Ca2+-binding affinities, that are expressed in CNT/CCD and may be regulated by TRPV4-mediated Ca2+influx. The K+-secreting CCD mCCDcl1 cells, which express these channels, were used to determine whether SK1/3 and IK1 are activated on TRPV4 stimulation and whether they contribute to Ca2+influx and activation of BK. Activation of TRPV4 (GSK1016790A) modestly depolarized the membrane potential and robustly increased intracellular Ca2+, [Ca2+]iInhibition of both SK1/3 and IK1 by application of apamin and 1-[(2-chlorophenyl)diphenylmethyl]-1H-pyrazole (TRAM-34), respectively, further depolarized the membrane potential and markedly suppressed the TRPV4-mediated rise in [Ca2+]iApplication of BK inhibitor iberiotoxin after activation of TRPV4 without apamin/TRAM-34 also reduced [Ca2+]iand further intensified membrane depolarization, demonstrating BK involvement. However, the BK-dependent effects on [Ca2+]iand membrane potential were largely abolished by pretreatment with apamin and TRAM-34, identical to that observed by separately suppressing TRPV4-mediated Ca2+influx, demonstrating that SK1/3-IK1 channels potently contribute to TRPV4-mediated BK activation. Our data indicate a direct correlation between TRPV4-mediated Ca2+signal and BK activation but where early activation of SK1/3 and IK1 channels are critical to sufficiently enhanced Ca2+entry and [Ca2+]ilevels required for activation of BK.
authors.affiliation: Department of Integrative Biology and Pharmacology, The University of Texas Health Science Center at Houston, Houston, Texas.
authors.forename: Yue
authors.initials: Y
authors.lastname: Li
authors.affiliation: Department of Integrative Biology and Pharmacology, The University of Texas Health Science Center at Houston, Houston, Texas.
authors.forename: Hongxiang
authors.initials: H
authors.lastname: Hu
authors.affiliation: Department of Integrative Biology and Pharmacology, The University of Texas Health Science Center at Houston, Houston, Texas.
authors.forename: Jin-Bin
authors.initials: JB
authors.lastname: Tian
authors.affiliation: Department of Integrative Biology and Pharmacology, The University of Texas Health Science Center at Houston, Houston, Texas.
authors.forename: Michael X
authors.initials: MX
authors.lastname: Zhu
authors.affiliation: Department of Integrative Biology and Pharmacology, The University of Texas Health Science Center at Houston, Houston, Texas roger.g.oneil@uth.tmc.edu.
authors.forename: Roger G
authors.initials: RG
authors.lastname: O'Neil
mesh_terms: D000818:Animals; D002118:Calcium / Q000378:metabolism*; D002120:Calcium Channel Agonists / Q000494:pharmacology; D020013:Calcium Signaling; D002478:Cells, Cultured; D051660:Intermediate-Conductance Calcium-Activated Potassium Channels / Q000037:antagonists & inhibitors / Q000378:metabolism*; D007685:Kidney Tubules, Collecting / Q000187:drug effects / Q000378:metabolism*; D051037:Large-Conductance Calcium-Activated Potassium Channel alpha Subunits / Q000037:antagonists & inhibitors / Q000378:metabolism*; D008564:Membrane Potentials; D051379:Mice; D011188:Potassium / Q000378:metabolism*; D026902:Potassium Channel Blockers / Q000494:pharmacology; D051640:Small-Conductance Calcium-Activated Potassium Channels / Q000037:antagonists & inhibitors / Q000378:metabolism*; D050916:TRPV Cation Channels / Q000819:agonists / Q000378:metabolism*
chemical_list: D002120:Calcium Channel Agonists; D051660:Intermediate-Conductance Calcium-Activated Potassium Channels; C465449:Kcnma1 protein, mouse; C496895:Kcnn1 protein, mouse; C496900:Kcnn3 protein, mouse; C496925:Kcnn4 protein, mouse; D051037:Large-Conductance Calcium-Activated Potassium Channel alpha Subunits; D026902:Potassium Channel Blockers; D051640:Small-Conductance Calcium-Activated Potassium Channels; D050916:TRPV Cation Channels; C486576:Trpv4 protein, mouse; D011188:Potassium; D002118:Calcium
keywords: BK (KCNMA1); IK1 (KCNN4); K+ secretion; KCa channels; SK1 (KCNN1); SK3 (KCNN3); TRPV4; cortical collecting duct; intracellular Ca2+; mCCDcl1 cells; membrane potential