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Length-dependent activation is modulated by cardiac troponin I bisphosphorylation at Ser23 and Ser24 but not by Thr143 phosphorylation

Authors :
Ger J.M. Stienen
Paul J.M. Wijnker
Vasco Sequeira
D. Brian Foster
Yuejin Li
Jolanda van der Velden
Anne M. Murphy
Cristobal G. dos Remedios
Physics of Living Systems
Physiology
ICaR - Heartfailure and pulmonary arterial hypertension
Source :
American Journal of Physiology. Heart and Circulatory Physiology, 306(8), H1171-H1181. American Physiological Society, Wijnker, P J M, Sequeira Oliveira, V, Foster, D B, Li, Y J, dos Remedios, C G, Murphy, A M, Stienen, G J M & van der Velden, J 2014, ' Length-dependent activation is modulated by cardiac troponin I bisphosphorylation at Ser23 and Ser24 but not by Thr143 phosphorylation ', American Journal of Physiology. Heart and Circulatory Physiology, vol. 306, no. 8, pp. H1171-H1181 . https://doi.org/10.1152/ajpheart.00580.2013
Publication Year :
2014

Abstract

Frank-Starling's law reflects the ability of the heart to adjust the force of its contraction to changes in ventricular filling, a property based on length-dependent myofilament activation (LDA). The threonine at amino acid 143 of cardiac troponin I (cTnI) is prerequisite for the length-dependent increase in Ca2+sensitivity. Thr143 is a known target of protein kinase C (PKC) whose activity is increased in cardiac disease. Thr143 phosphorylation may modulate length-dependent myofilament activation in failing hearts. Therefore, we investigated if pseudo-phosphorylation at Thr143 modulates length dependence of force using troponin exchange experiments in human cardiomyocytes. In addition, we studied effects of protein kinase A (PKA)-mediated cTnI phosphorylation at Ser23/24, which has been reported to modulate LDA. Isometric force was measured at various Ca2+concentrations in membrane-permeabilized cardiomyocytes exchanged with recombinant wild-type (WT) troponin or troponin mutated at the PKC site Thr143 or Ser23/24 into aspartic acid (D) or alanine (A) to mimic phosphorylation and dephosphorylation, respectively. In troponin-exchanged donor cardiomyocytes experiments were repeated after incubation with exogenous PKA. Pseudo-phosphorylation of Thr143 increased myofilament Ca2+sensitivity compared with WT without affecting LDA in failing and donor cardiomyocytes. Subsequent PKA treatment enhanced the length-dependent shift in Ca2+sensitivity after WT and 143D exchange. Exchange with Ser23/24 variants demonstrated that pseudo-phosphorylation of both Ser23 and Ser24 is needed to enhance the length-dependent increase in Ca2+sensitivity. cTnI pseudo-phosphorylation did not alter length-dependent changes in maximal force. Thus phosphorylation at Thr143 enhances myofilament Ca2+sensitivity without affecting LDA, while Ser23/24 bisphosphorylation is needed to enhance the length-dependent increase in myofilament Ca2+sensitivity.

Details

ISSN :
03636135
Volume :
306
Issue :
8
Database :
OpenAIRE
Journal :
American Journal of Physiology. Heart and Circulatory Physiology
Accession number :
edsair.doi.dedup.....86961ce19c606cad85a9b8f20ca84a37