Faculty Collaboration Database

Effects of the mutation R145G in human cardiac troponin I on the kinetics of the contraction-relaxation cycle in isolated cardiac myofibrils. J Physiol 2005 Apr 15;564(Pt 2):347-57

Date

02/19/2005

Pubmed ID

15718266

Pubmed Central ID

PMC1464436

DOI

10.1113/jphysiol.2004.079095

Scopus ID

2-s2.0-17844363735 (requires institutional sign-in at Scopus site)   45 Citations

Abstract

Familial hypertrophic cardiomyopathy (FHC) has been linked to mutations in sarcomeric proteins such as human cardiac troponin I (hcTnI). To elucidate the functional consequences of the mutation hcTnI(R145G) on crossbridge kinetics, force kinetics were analysed in murine cardiac myofibrils carrying either the mutant or the wild-type protein. The mutation was introduced into the myofibrils in two different ways: in the first approach, the endogenous Tn was replaced by incubation of the myofibrils with an excess of reconstituted recombinant hcTn containing either hcTnI(WT) or hcTnI(R145G). Alternatively, myofibrils were isolated either from non-transgenic or transgenic mice expressing the corresponding mcTnI(R146G) mutation. In myofibrils from both models, the mutation leads to a significant upward shift of the passive force-sarcomere length relation determined at pCa 7.5. Addition of 5 mm BDM (2,3-butandione-2-monoxime), an inhibitor of actomyosin ATPase partially reverses this shift, suggesting that the mutation impairs the normal function of cTnI to fully inhibit formation of force-generating crossbridges in the absence of Ca(2)(+). Maximum force development (F(max)) is significantly decreased by the mutation only in myofibrils exchanged with hcTnI(R145G) in vitro. Ca(2)(+) sensitivity of force development was reduced by the mutation in myofibrils from transgenic mice but not in exchanged myofibrils. In both models the rate constant of force development k(ACT) is reduced at maximal [Ca(2)(+)] but not at low [Ca(2)(+)] where it is rather increased. Force relaxation is significantly prolonged due to a reduction of the relaxation rate constant k(REL). We therefore assume that the impairment in the regulatory function of TnI by the mutation leads to modulations in crossbridge kinetics that significantly alter the dynamics of myofibrillar contraction and relaxation.

Author List

Kruger M, Zittrich S, Redwood C, Blaudeck N, James J, Robbins J, Pfitzer G, Stehle R

MESH terms used to index this publication - Major topics in bold

Animals
Arginine
Glycine
Humans
Kinetics
Mice
Mice, Transgenic
Muscle Contraction
Muscle Relaxation
Mutation
Myocardium
Myofibrils
Troponin I