title: Molecular and functional significance of Ca(2+)-activated Cl(-) channels in pulmonary arterial smooth muscle.
abstract: Increased peripheral resistance of small distal pulmonary arteries is a hallmark signature of pulmonary hypertension (PH) and is believed to be the consequence of enhanced vasoconstriction to agonists, thickening of the arterial wall due to remodeling, and increased thrombosis. The elevation in arterial tone in PH is attributable, at least in part, to smooth muscle cells of PH patients being more depolarized and displaying higher intracellular Ca(2+) levels than cells from normal subjects. It is now clear that downregulation of voltage-dependent K(+) channels (e.g., Kv1.5) and increased expression and activity of voltage-dependent (Cav1.2) and voltage-independent (e.g., canonical and vanilloid transient receptor potential [TRPC and TRPV]) Ca(2+) channels play an important role in the functional remodeling of pulmonary arteries in PH. This review focuses on an anion-permeable channel that is now considered a novel excitatory mechanism in the systemic and pulmonary circulations. It is permeable to Cl(-) and is activated by a rise in intracellular Ca(2+) concentration (Ca(2+)-activated Cl(-) channel, or CaCC). The first section outlines the biophysical and pharmacological properties of the channel and ends with a description of the molecular candidate genes postulated to encode for CaCCs, with particular emphasis on the bestrophin and the newly discovered TMEM16 and anoctamin families of genes. The second section provides a review of the various sources of Ca(2+) activating CaCCs, which include stimulation by mobilization from intracellular Ca(2+) stores and Ca(2+) entry through voltage-dependent and voltage-independent Ca(2+) channels. The third and final section summarizes recent findings that suggest a potentially important role for CaCCs and the gene TMEM16A in PH.
authors.affiliation: Department of Pharmacology, University of Nevada School of Medicine, Reno, Nevada, USA.
authors.forename: Normand
authors.initials: N
authors.lastname: Leblanc
authors.affiliation: Department of Pharmacology, University of Nevada School of Medicine, Reno, Nevada, USA.
authors.forename: Abigail S
authors.initials: AS
authors.lastname: Forrest
authors.affiliation: Department of Medicine, University of Illinois, Chicago, Illinois, USA.
authors.forename: Ramon J
authors.initials: RJ
authors.lastname: Ayon
authors.affiliation: Department of Pharmacology, University of Nevada School of Medicine, Reno, Nevada, USA.
authors.forename: Michael
authors.initials: M
authors.lastname: Wiwchar
authors.affiliation: School of Community Health Sciences, University of Nevada, Reno, Nevada, USA.
authors.forename: Jeff E
authors.initials: JE
authors.lastname: Angermann
authors.affiliation: Vascular Biology Research Centre, Institute of Cardiovascular and Cell Sciences, St. George's University of London, London, United Kingdom.
authors.forename: Harry A T
authors.initials: HA
authors.lastname: Pritchard
authors.affiliation: Department of Pharmacology, University of Nevada School of Medicine, Reno, Nevada, USA.
authors.forename: Cherie A
authors.initials: CA
authors.lastname: Singer
authors.affiliation: Department of Biochemistry and Molecular Biology, University of Nevada School of Medicine, Reno, Nevada, USA.
authors.forename: Maria L
authors.initials: ML
authors.lastname: Valencik
authors.affiliation: Department of Physiology, School of Medical Sciences, University of New South Wales, Sydney, Australia.
authors.forename: Fiona
authors.initials: F
authors.lastname: Britton
authors.affiliation: Vascular Biology Research Centre, Institute of Cardiovascular and Cell Sciences, St. George's University of London, London, United Kingdom.
authors.forename: Iain A
authors.initials: IA
authors.lastname: Greenwood
keywords: TMEM16A; anoctamin; bestrophin; calcium-activated chloride channels; pulmonary hypertension