Functional effects of a restrictive-cardiomyopathy-linked cardiac troponin I mutation (R145W) in transgenic mice.
The human cardiac troponin I (hcTnI) mutation R145W has been associated with restrictive cardiomyopathy. In this study, simultaneous measurements of ATPase activity and force in skinned papillary fibers from hcTnI R145W transgenic mice (Tg-R145W) were explored. Tg-R145W fibers showed an approximately 13-16% increase in maximal Ca(2+)-activated force and ATPase activity compared to hcTnI wild-type transgenic mice. The force-generating cross-bridge turnover rate (g) and the energy cost (ATPase/force) were the same in all groups of fibers. Also, the Tg-R145W fibers showed a large increase in the Ca(2+) sensitivity of both force development and ATPase. In intact fibers, the mutation caused prolonged force and intracellular [Ca(2+)] transients and increased time to peak force. Analysis of force and Ca(2+) transients showed that there was a 40% increase in peak force in Tg-R145W muscles, which was likely due to the increased Ca(2+) transient duration. The above cited results suggest that: (1) there would be an increase in resistance to ventricular filling during diastole resulting from the prolonged force and Ca(2+) transients that would result in a decrease in ventricular filling (diastolic dysfunction); and (2) there would be a large (approximately 53%) increase in force during systole, which may help to partly compensate for diastolic dysfunction. These functional results help to explain the mechanisms by which these mutations give rise to a restrictive phenotype.
Wen
Yuhui
Y
Department of Physiology and Biophysics, Miller School of Medicine, University of Miami, Miami, FL 33136, USA.
Xu
Yuanyuan
Y
Wang
Yingcai
Y
Pinto
Jose Renato
JR
Potter
James D
JD
Kerrick
W Glenn L
WG
D000255:Adenosine Triphosphate / Q000378:metabolism; D019943:Amino Acid Substitution / Q000235:genetics*; D000818:Animals; D002313:Cardiomyopathy, Restrictive / Q000235:genetics*; D006801:Humans; D051379:Mice; D008822:Mice, Transgenic; D020125:Mutation, Missense; D009200:Myocardial Contraction; D009210:Myofibrils / Q000502:physiology; D019210:Troponin I / Q000235:genetics*
D019210:Troponin I; D000255:Adenosine Triphosphate