title: Changes in cardiac troponins with gestational age explain changes in cardiac muscle contractility in the sheep fetus.
abstract: The development of the adult cardiac troponin complex in conjunction with changes in cardiac function and cardiomyocyte binucleation has not been systematically characterized during fetal life in a species where maturation of the cardiomyocytes occurs prenatally as it does in the human. The aim of this study was to correlate the expression of each of the major adult troponin isoforms (T, I, and C) during late gestation (term of 150 days) to changes in both Ca(2+) sensitivity and maximum Ca(2+)-activated force of the contractile apparatus and the maturation of cardiomyocytes. The percentage of mononucleated cardiomyocytes in the right ventricle decreased with gestational age to 46% by 137-142 days of gestation. The length of binucleated cardiomyocytes did not change with gestational age, but the length of binucleated cardiomyocytes relative to heart weight decreased with gestational age. There was no change in the expression of adult cardiac troponin T with increasing gestation. The contractile apparatus was significantly more sensitive to Ca(2+) at 90 days compared with either 132 or 139 days of gestation, consistent with an ∼30% increase in the expression of adult cardiac troponin I between 90 and 110 days of gestation. Maximum Ca(2+)-activated force significantly increased from 90 days compared with 130 days consistent with an increase of ∼40% in cardiac troponin C protein expression. These data show that increased adult cardiac troponin I and C protein expression across late gestation is consistent with reduced Ca(2+) sensitivity and increased maximum Ca(2+)-activated force. Furthermore, changes in cardiac troponin C, not I, protein expression track with the timing of cardiomyocyte binucleation.
authors.affiliation: Department of Zoology, School of Life Sciences, Faculty of Science and Technology, LaTrobe University, Melbourne, VIC, Australia. g.posterino@latrobe.edu.au
authors.forename: Giuseppe Saverio
authors.initials: GS
authors.lastname: Posterino
authors.forename: Stacey Leanne
authors.initials: SL
authors.lastname: Dunn
authors.forename: Kimberley Jae
authors.initials: KJ
authors.lastname: Botting
authors.forename: William
authors.initials: W
authors.lastname: Wang
authors.forename: Sheridan
authors.initials: S
authors.lastname: Gentili
authors.forename: Janna Leigh
authors.initials: JL
authors.lastname: Morrison
mesh_terms: D000818:Animals; D056966:Excitation Contraction Coupling; D005318:Fetal Heart / Q000378:metabolism*; D005865:Gestational Age; D053580:Muscle Strength; D009200:Myocardial Contraction; D032383:Myocytes, Cardiac / Q000378:metabolism*; D012756:Sheep; D014336:Troponin / Q000378:metabolism*; D019209:Troponin C / Q000378:metabolism; D019210:Troponin I / Q000378:metabolism; D020107:Troponin T / Q000378:metabolism
chemical_list: D014336:Troponin; D019209:Troponin C; D019210:Troponin I; D020107:Troponin T