title: Calcium-independent activation of skinned cardiac muscle by secophalloidin.
abstract: Thin filament regulation of muscle contraction is believed to be mediated by both Ca2+ and strongly bound myosin cross-bridges. We found that secophalloidin (SPH, 5-8 mM) activates cross-bridge cycling without Ca2+ causing isometric force comparable to that induced by Ca2+. At saturated [SPH], Ca2+ further increased force by 20%. SPH-induced force was reversible upon washing with a relaxing solution. However, there was more than 30% irreversible loss in subsequent Ca2+-activated force. We hypothesize that SPH activates muscle via strongly bound cross-bridges. SPH-activated contraction provides a new model for studying the role of Ca2+ and cross-bridges in muscle regulation.
authors.affiliation: Departments of Anesthesiology, and Physiology and Biophysics, Mayo Foundation, Jo 4-184, 200 First Street SW, Rochester, MN 55905, USA. bukatina.anna@mayo.edu
authors.forename: Anna E
authors.initials: AE
authors.lastname: Bukatina
authors.forename: Lou J
authors.initials: LJ
authors.lastname: Theodore
authors.forename: Kenneth B
authors.initials: KB
authors.lastname: Campbell
authors.forename: Gary C
authors.initials: GC
authors.lastname: Sieck
mesh_terms: D000199:Actins / Q000378:metabolism; D000818:Animals; D002118:Calcium / Q000378:metabolism*; D002417:Cattle; D006352:Heart Ventricles / Q000187:drug effects* / Q000378:metabolism*; D066298:In Vitro Techniques; D007537:Isometric Contraction / Q000187:drug effects; D009200:Myocardial Contraction / Q000187:drug effects; D009206:Myocardium / Q000378:metabolism*; D010590:Phalloidine / Q000031:analogs & derivatives / Q000737:chemistry / Q000494:pharmacology*; D013314:Stress, Mechanical; D013329:Structure-Activity Relationship; D019209:Troponin C / Q000737:chemistry / Q000378:metabolism
chemical_list: D000199:Actins; D019209:Troponin C; C456940:secophalloidin-H-A; D010590:Phalloidine; D002118:Calcium