title: Thyroxine induces transition of red towards white muscle in cultured heart cells.
abstract: Thyroid hormones (TH) have previously been shown to alter the force and velocity of cardiac muscle contractions. To investigate the mechanism responsible for these alterations, excess amounts of thyroxine (T4, 1 microM) were applied on rat heart cells grown in cell culture. We found the following biochemical alterations: a) 40% decrease in the myoglobin content within 2 days; b) 25% increase in the rate of Ca-uptake into sacroplasmic reticulum (SR) in myocytes following chemical skinning; and c) a two-fold increase in Na-K-ATPase activity measured by 86Rb-uptake. These changes support our hypothesis that TH induce the transition of slow-twitch ("red") muscles towards the fast-twitch ("white") muscle type. This may explain the changes in contractile activity known to occur under TH influence.
authors.affiliation: Department of Life Sciences, Bar-Ilan University, Ramat-Gan, Israel.
authors.forename: H
authors.initials: H
authors.lastname: Brik
authors.forename: A
authors.initials: A
authors.lastname: Shainberg
mesh_terms: D000818:Animals; D002118:Calcium / Q000378:metabolism; D002478:Cells, Cultured; D006321:Heart / Q000187:drug effects; D008855:Microscopy, Electron, Scanning; D009200:Myocardial Contraction / Q000187:drug effects; D009206:Myocardium / Q000378:metabolism*; D009211:Myoglobin / Q000378:metabolism; D051381:Rats; D012414:Rubidium Radioisotopes / Q000378:metabolism; D012519:Sarcoplasmic Reticulum / Q000378:metabolism; D000254:Sodium-Potassium-Exchanging ATPase / Q000378:metabolism; D013974:Thyroxine / Q000494:pharmacology*
chemical_list: D009211:Myoglobin; D012414:Rubidium Radioisotopes; D000254:Sodium-Potassium-Exchanging ATPase; D013974:Thyroxine; D002118:Calcium