Document Detail

Developmental changes in passive stiffness and myofilament Ca2+ sensitivity due to titin and troponin-I isoform switching are not critically triggered by birth.
MedLine Citation:
PMID:  16679402     Owner:  NLM     Status:  MEDLINE    
The giant protein titin, a major contributor to myocardial mechanics, is expressed in two main cardiac isoforms: stiff N2B (3.0 MDa) and more compliant N2BA (>3.2 MDa). Fetal hearts of mice, rats, and pigs express a unique N2BA isoform ( approximately 3.7 MDa) but no N2B. Around birth the fetal N2BA titin is replaced by smaller-size N2BA isoforms and N2B, which predominates in adult hearts, stiffening their sarcomeres. Here we show that perinatal titin-isoform switching and corresponding passive stiffness (STp) changes do not occur in the hearts of guinea pig and sheep. In these species the shift toward "adult" proportions of N2B isoform is almost completed by midgestation. The relative contributions of titin and collagen to STp were estimated in force measurements on skinned cardiac muscle strips by selective titin proteolysis, leaving the collagen matrix unaffected. Titin-based STp contributed between 42% and 58% to total STp in late-fetal and adult sheep/guinea pigs and adult rats. However, only approximately 20% of total STp was titin based in late-fetal rat. Titin-borne passive tension and the proportion of titin-based STp generally scaled with the N2B isoform percentage. The titin isoform transitions were correlated to a switch in troponin-I (TnI) isoform expression. In rats, fetal slow skeletal TnI (ssTnI) was replaced by adult carciac TnI (cTnI) shortly after birth, thereby reducing the Ca2+ sensitivity of force development. In contrast, guinea pig and sheep coexpressed ssTnI and cTnI in fetal hearts, and skinned fibers from guinea pig showed almost no perinatal shift in Ca2+ sensitivity. We conclude that TnI-isoform and titin-isoform switching and corresponding functional changes during heart development are not initiated by birth but are genetically programmed, species-specific regulated events.
Martina Krüger; Thomas Kohl; Wolfgang A Linke
Publication Detail:
Type:  Journal Article; Research Support, Non-U.S. Gov't     Date:  2006-05-05
Journal Detail:
Title:  American journal of physiology. Heart and circulatory physiology     Volume:  291     ISSN:  0363-6135     ISO Abbreviation:  Am. J. Physiol. Heart Circ. Physiol.     Publication Date:  2006 Aug 
Date Detail:
Created Date:  2006-07-14     Completed Date:  2006-08-18     Revised Date:  2009-11-19    
Medline Journal Info:
Nlm Unique ID:  100901228     Medline TA:  Am J Physiol Heart Circ Physiol     Country:  United States    
Other Details:
Languages:  eng     Pagination:  H496-506     Citation Subset:  IM    
Physiology and Biophysics Unit, Univ. of Muenster, Schlossplatz 5, D-48149 Muenster, Germany.
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MeSH Terms
Animals, Newborn
Blotting, Western
Calcium / physiology*
Collagen / metabolism
Electrophoresis, Polyacrylamide Gel
Guinea Pigs
Heart / growth & development*,  physiology*
Microfilaments / physiology*
Microscopy, Electron, Transmission
Muscle Proteins / metabolism,  physiology*
Myocardial Contraction / physiology
Myocardium / cytology,  metabolism,  ultrastructure
Myocytes, Cardiac / physiology,  ultrastructure
Parturition / physiology*
Protein Kinases / metabolism,  physiology*
Rats, Sprague-Dawley
Troponin I / metabolism,  physiology*
Reg. No./Substance:
0/Muscle Proteins; 0/Troponin I; 0/connectin; 7440-70-2/Calcium; 9007-34-5/Collagen; EC 2.7.-/Protein Kinases
Erratum In:
Am J Physiol Heart Circ Physiol. 2007 Jan;292(1):H726

From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine

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