title: Chloroform extract of hog barn dust modulates skeletal muscle ryanodine receptor calcium-release channel (RyR1).
abstract: Skeletal muscle weakness is a reported ailment in individuals working in commercial hog confinement facilities. To date, specific mechanisms responsible for this symptom remain undefined. The purpose of this study was to assess whether hog barn dust (HBD) contains components that are capable of binding to and modulating the activity of type 1 ryanodine receptor Ca2+-release channel (RyR1), a key regulator of skeletal muscle function. HBD collected from confinement facilities in Nebraska were extracted with chloroform, filtered, and rotary evaporated to dryness. Residues were resuspended in hexane-chloroform (20:1) and precipitates, referred to as HBDorg, were air-dried and studied further. In competition assays, HBDorg dose-dependently displaced [3H]ryanodine from binding sites on RyR1 with an IC50 of 1.5±0.1 microg/ml (Ki=0.4±0.0 microg/ml). In single-channel assays using RyR1 reconstituted into a lipid bilayer, HBDorg exhibited three distinct dose-dependent effects: first it increased the open probability of RyR1 by increasing its gating frequency and dwell time in the open state, then it induced a state of reduced conductance (55% of maximum) that was more likely to occur and persist at positive holding potentials, and finally it irreversibly closed RyR1. In differentiated C2C12 myotubes, addition of HBD triggered a rise in intracellular Ca2+ that was blocked by pretreatment with ryanodine. Since persistent activation and/or closure of RyR1 results in skeletal muscle weakness, these new data suggest that HBD is responsible, at least in part, for the muscle ailment reported by hog confinement workers.
authors.affiliation: Department of Pharmacology and Experimental Neuroscience, University of Nebraska Medical Center, Omaha, NE 68198-5800, USA.
authors.forename: Chengju
authors.initials: C
authors.lastname: Tian
authors.forename: Chun Hong
authors.initials: CH
authors.lastname: Shao
authors.forename: Danielle S
authors.initials: DS
authors.lastname: Fenster
authors.forename: Mark
authors.initials: M
authors.lastname: Mixan
authors.forename: Debra J
authors.initials: DJ
authors.lastname: Romberger
authors.forename: Myron L
authors.initials: ML
authors.lastname: Toews
authors.forename: Keshore R
authors.initials: KR
authors.lastname: Bidasee
mesh_terms: D000382:Agricultural Workers' Diseases / Q000139:chemically induced; D000818:Animals; D001665:Binding Sites; D001667:Binding, Competitive; D002118:Calcium / Q000378:metabolism; D002120:Calcium Channel Agonists / Q000009:adverse effects / Q000302:isolation & purification / Q000378:metabolism / Q000494:pharmacology*; D002121:Calcium Channel Blockers / Q000009:adverse effects / Q000302:isolation & purification / Q000378:metabolism / Q000494:pharmacology*; D002460:Cell Line; D002725:Chloroform / Q000737:chemistry*; D002855:Chromatography, Thin Layer; D004305:Dose-Response Relationship, Drug; D004391:Dust / Q000032:analysis*; D006799:Housing, Animal; D006801:Humans; D015640:Ion Channel Gating / Q000187:drug effects*; D008564:Membrane Potentials; D051379:Mice; D018485:Muscle Fibers, Skeletal / Q000187:drug effects / Q000378:metabolism; D018908:Muscle Weakness / Q000139:chemically induced; D018482:Muscle, Skeletal / Q000187:drug effects* / Q000378:metabolism; D016272:Occupational Health; D011817:Rabbits; D018570:Risk Assessment; D012433:Ryanodine / Q000378:metabolism; D019837:Ryanodine Receptor Calcium Release Channel / Q000187:drug effects* / Q000378:metabolism; D012997:Solvents / Q000737:chemistry*; D034421:Sus scrofa
chemical_list: D002120:Calcium Channel Agonists; D002121:Calcium Channel Blockers; D004391:Dust; D019837:Ryanodine Receptor Calcium Release Channel; D012997:Solvents; D012433:Ryanodine; D002725:Chloroform; D002118:Calcium