title: Drop in endo/sarcoplasmic calcium precedes the unfolded protein response in Brefeldin A-treated vascular smooth muscle cells.
abstract: The present study addresses the causal relationship between induction of endo/sarcoplasmic reticulum stress and dysregulation of calcium transport, while examining whether the most widely-used experimental endo/sarcoplasmic reticulum stressors can be considered appropriate for elucidating underlying cellular mechanisms involved during the progression of the unfolded protein response in vascular smooth muscle cells. Brefeldin A is most commonly cited as inducing the stress response through an accumulation of unfolded proteins in the lumen as a result of a blockage of protein transport from the endo/sarcoplasmic reticulum to the Golgi apparatus. We investigated the effects of Brefeldin A on cellular calcium regulation during the the unfolded protein response in cultured rat vascular smooth muscle cells. Acute exposure of cells to Brefeldin A caused a small transient increase in cytoplasmic calcium, which did not cause a significant decrease in endo/sarcoplasmic reticulum calcium content. However, over the time course of 0-12 h post-treatment with Brefeldin A, we observed that the endo/sarcoplasmic reticulum of vascular smooth muscle cells exhibited an approximate fifty percent decrease in calcium concentration after the first hour of exposure, which is maintained over the next eleven hours, whereas concentrations of unfolded protein response markers only began to increase significantly around nine to twelve hours post-treatment. We have concluded that the endo/sarcoplasmic reticulum calcium drop, which up to now, has been considered as a characteristic of the late onset of cellular stress response, occurs prior to the initiation of the unfolded protein response, rather than as a result of its many corrective pathways.
authors.affiliation: Child & Family Research Institute, Department of Anaesthesiology, Pharmacology, and Therapeutics, University of British Columbia, Vancouver, British Columbia, Canada.
authors.forename: Gabriela
authors.initials: G
authors.lastname: Ziomek
authors.affiliation: Child & Family Research Institute, Department of Anaesthesiology, Pharmacology, and Therapeutics, University of British Columbia, Vancouver, British Columbia, Canada. Electronic address: casey@ti.ubc.ca.
authors.forename: Cornelis
authors.initials: C
authors.lastname: van Breemen
authors.affiliation: Child & Family Research Institute, Department of Anaesthesiology, Pharmacology, and Therapeutics, University of British Columbia, Vancouver, British Columbia, Canada; Department of Biomedical Sciences, College of Health Sciences, Midwestern University, Glendale, AZ, USA. Electronic address: mesfan@midwestern.edu.
authors.forename: Mitra
authors.initials: M
authors.lastname: Esfandiarei
mesh_terms: D000818:Animals; D020126:Brefeldin A / Q000494:pharmacology*; D002118:Calcium / Q000378:metabolism*; D002478:Cells, Cultured; D004305:Dose-Response Relationship, Drug; D004721:Endoplasmic Reticulum / Q000187:drug effects* / Q000378:metabolism; D059865:Endoplasmic Reticulum Stress / Q000187:drug effects; D008297:Male; D008931:Mitochondria, Muscle / Q000187:drug effects / Q000378:metabolism; D009131:Muscle, Smooth, Vascular / Q000187:drug effects* / Q000378:metabolism; D032389:Myocytes, Smooth Muscle / Q000187:drug effects* / Q000378:metabolism; D011921:Rats, Inbred WKY; D012519:Sarcoplasmic Reticulum / Q000187:drug effects* / Q000378:metabolism; D013997:Time Factors; D056811:Unfolded Protein Response / Q000187:drug effects*
chemical_list: D020126:Brefeldin A; D002118:Calcium
keywords: Brefeldin A; Calcium; ER stress; Unfolded protein response; Vascular smooth muscle cells