title: Modulation of CFTR gating by permeant ions.
abstract: Cystic fibrosis transmembrane conductance regulator (CFTR) is unique among ion channels in that after its phosphorylation by protein kinase A (PKA), its ATP-dependent gating violates microscopic reversibility caused by the intimate involvement of ATP hydrolysis in controlling channel closure. Recent studies suggest a gating model featuring an energetic coupling between opening and closing of the gate in CFTR's transmembrane domains and association and dissociation of its two nucleotide-binding domains (NBDs). We found that permeant ions such as nitrate can increase the open probability (Po) of wild-type (WT) CFTR by increasing the opening rate and decreasing the closing rate. Nearly identical effects were seen with a construct in which activity does not require phosphorylation of the regulatory domain, indicating that nitrate primarily affects ATP-dependent gating steps rather than PKA-dependent phosphorylation. Surprisingly, the effects of nitrate on CFTR gating are remarkably similar to those of VX-770 (N-(2,4-Di-tert-butyl-5-hydroxyphenyl)-4-oxo-1,4-dihydroquinoline-3-carboxamide), a potent CFTR potentiator used in clinics. These include effects on single-channel kinetics of WT CFTR, deceleration of the nonhydrolytic closing rate, and potentiation of the Po of the disease-associated mutant G551D. In addition, both VX-770 and nitrate increased the activity of a CFTR construct lacking NBD2 (ΔNBD2), indicating that these gating effects are independent of NBD dimerization. Nonetheless, whereas VX-770 is equally effective when applied from either side of the membrane, nitrate potentiates gating mainly from the cytoplasmic side, implicating a common mechanism for gating modulation mediated through two separate sites of action.
authors.affiliation: Physician-Scientist Program, School of Medicine, National Yang-Ming University, Taipei, 112 Taiwan Dalton Cardiovascular Research Center and Department of Medical Pharmacology and Physiology, University of Missouri, Columbia, MO 65211.
authors.forename: Han-I
authors.initials: HI
authors.lastname: Yeh
authors.affiliation: Physician-Scientist Program, School of Medicine, National Yang-Ming University, Taipei, 112 Taiwan Dalton Cardiovascular Research Center and Department of Medical Pharmacology and Physiology, University of Missouri, Columbia, MO 65211.
authors.forename: Jiunn-Tyng
authors.initials: JT
authors.lastname: Yeh
authors.affiliation: Dalton Cardiovascular Research Center and Department of Medical Pharmacology and Physiology, University of Missouri, Columbia, MO 65211 Dalton Cardiovascular Research Center and Department of Medical Pharmacology and Physiology, University of Missouri, Columbia, MO 65211 hwangt@health.missouri.edu.
authors.forename: Tzyh-Chang
authors.initials: TC
authors.lastname: Hwang
mesh_terms: D000627:Aminophenols / Q000494:pharmacology; D000818:Animals; D016466:CHO Cells; D006224:Cricetinae; D003412:Cricetulus; D019005:Cystic Fibrosis Transmembrane Conductance Regulator / Q000737:chemistry / Q000187:drug effects / Q000378:metabolism*; D015640:Ion Channel Gating / Q000187:drug effects*; D020125:Mutation, Missense; D009566:Nitrates / Q000494:pharmacology*; D017434:Protein Structure, Tertiary; D015363:Quinolones / Q000494:pharmacology
chemical_list: D000627:Aminophenols; D009566:Nitrates; D015363:Quinolones; D019005:Cystic Fibrosis Transmembrane Conductance Regulator; C545203:ivacaftor