title: Myosin-based contraction is not necessary for cardiac c-looping in the chick embryo.
abstract: During the initial phase of cardiac looping, known as c-looping, the heart bends and twists into a c-shaped tube with the convex outer curvature normally directed toward the right side of the embryo. Despite intensive study for more than 80 years, the biophysical mechanisms that drive and regulate looping remain poorly understood, although some investigators have speculated that differential cytoskeletal contraction supplies the driving force for c-looping. The purpose of this investigation was to test this hypothesis. To inhibit contraction, embryonic chick hearts at stages 10-12 (10-16 somites, 33-48 h) were exposed to the myosin inhibitors 2,3-butanedione monoxime (BDM), ML-7, Y-27632, and blebbistatin. Experiments were conducted in both whole embryo culture and, to focus on bending alone, isolated heart culture. Measurements of heart stiffness and phosphorylation of the myosin regulatory light chains showed that BDM, Y-27632, and blebbistatin significantly reduced myocardial contractility, while ML-7 had a lesser effect. None of these drugs significantly affected looping during the studied stages. These results suggest that active contraction is not required for normal c-looping of the embryonic chick heart between stages 10 and 12.
authors.affiliation: Department of Biomedical Engineering, Washington University, Campus Box 1097, St Louis, MO 63130, USA.
authors.forename: Mathieu C
authors.initials: MC
authors.lastname: Rémond
authors.forename: Judy A
authors.initials: JA
authors.lastname: Fee
authors.forename: Elliot L
authors.initials: EL
authors.lastname: Elson
authors.forename: Larry A
authors.initials: LA
authors.lastname: Taber
mesh_terms: D000577:Amides / Q000494:pharmacology; D000818:Animals; D001381:Azepines / Q000494:pharmacology; D002642:Chick Embryo; D002645:Chickens; D003599:Cytoskeleton / Q000502:physiology; D003931:Diacetyl / Q000031:analogs & derivatives / Q000494:pharmacology; D004791:Enzyme Inhibitors / Q000494:pharmacology; D006321:Heart / Q000196:embryology* / Q000502:physiology*; D006576:Heterocyclic Compounds, 4 or More Rings / Q000494:pharmacology; D009200:Myocardial Contraction / Q000187:drug effects / Q000502:physiology*; D018994:Myosin Light Chains / Q000037:antagonists & inhibitors / Q000378:metabolism*; D009281:Naphthalenes / Q000494:pharmacology; D009924:Organ Culture Techniques; D010766:Phosphorylation; D011725:Pyridines / Q000494:pharmacology; D019170:Somites / Q000187:drug effects / Q000502:physiology; D014102:Torsion Abnormality
chemical_list: D000577:Amides; D001381:Azepines; D004791:Enzyme Inhibitors; D006576:Heterocyclic Compounds, 4 or More Rings; D018994:Myosin Light Chains; D009281:Naphthalenes; D011725:Pyridines; C070571:ML 7; C108830:Y 27632; C004717:diacetylmonoxime; C472645:blebbistatin; D003931:Diacetyl