title: Divergent effects of α- and β-myosin heavy chain isoforms on the N terminus of rat cardiac troponin T.
abstract: Divergent effects of α- and β-myosin heavy chain (MHC) isoforms on contractile behavior arise mainly because of their impact on thin filament cooperativity. The N terminus of cardiac troponin T (cTnT) also modulates thin filament cooperativity. Our hypothesis is that the impact of the N terminus of cTnT on thin filament activation is modulated by a shift from α- to β-MHC isoform. We engineered two recombinant proteins by deleting residues 1-43 and 44-73 in rat cTnT (RcTnT): RcTnT(1-43Δ) and RcTnT(44-73Δ), respectively. Dynamic and steady-state contractile parameters were measured at sarcomere length of 2.3 µm after reconstituting proteins into detergent-skinned muscle fibers from normal (α-MHC) and propylthiouracil-treated (β-MHC) rat hearts. α-MHC attenuated Ca(2+)-activated maximal tension (∼46%) in RcTnT(1-43Δ) fibers. In contrast, β-MHC decreased tension only by 19% in RcTnT(1-43Δ) fibers. Both α- and β-MHC did not affect tension in RcTnT(44-73Δ) fibers. The instantaneous muscle fiber stiffness measurements corroborated the divergent impact of α- and β-MHC on tension in RcTnT(1-43Δ) fibers. pCa50 (-log of [Ca(2+)]free required for half-maximal activation) decreased significantly by 0.13 pCa units in α-MHC + RcTnT(1-43Δ) fibers but remained unaltered in β-MHC + RcTnT(1-43Δ) fibers, demonstrating that β-MHC counteracted the attenuating effect of RcTnT(1-43Δ) on myofilament Ca(2+) sensitivity. β-MHC did not alter the sudden stretch-mediated recruitment of new cross-bridges (ER) in RcTnT(1-43Δ) fibers, but α-MHC attenuated ER by 36% in RcTnT(1-43Δ) fibers. The divergent impact of α- and β-MHC on how the N terminus of cTnT modulates contractile dynamics has implications for heart disease; alterations in cTnT and MHC are known to occur via changes in isoform expression or mutations.
authors.affiliation: Department of Integrative Physiology and Neuroscience, Washington State University, Pullman, WA 99164.
authors.forename: Ranganath
authors.initials: R
authors.lastname: Mamidi
authors.forename: Murali
authors.initials: M
authors.lastname: Chandra
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D002118:Calcium / Q000378:metabolism; D008297:Male; D008969:Molecular Sequence Data; D009119:Muscle Contraction; D009154:Mutation; D018995:Myosin Heavy Chains / Q000378:metabolism*; D011441:Propylthiouracil / Q000494:pharmacology; D020033:Protein Isoforms / Q000378:metabolism; D017434:Protein Structure, Tertiary; D051381:Rats; D017207:Rats, Sprague-Dawley; D012518:Sarcomeres / Q000187:drug effects / Q000378:metabolism / Q000502:physiology*; D020107:Troponin T / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D024723:Ventricular Myosins / Q000378:metabolism*
chemical_list: D020033:Protein Isoforms; D020107:Troponin T; D011441:Propylthiouracil; D024723:Ventricular Myosins; D018995:Myosin Heavy Chains; D002118:Calcium
references.citation: Adv Exp Med Biol. 2007;592:177-89
references.pmid: 17278365
references.citation: J Mol Cell Cardiol. 1999 Apr;31(4):867-80
references.pmid: 10329214
references.citation: Circ Res. 2004 May 28;94(10):1290-300
references.pmid: 15166116
references.citation: Am J Physiol Heart Circ Physiol. 2005 Feb;288(2):H896-903
references.pmid: 15471982
references.citation: J Physiol. 2001 Oct 15;536(Pt 2):583-92
references.pmid: 11600691
references.citation: Arch Biochem Biophys. 2011 Jan 15;505(2):144-54
references.pmid: 20965144
references.citation: Circ Res. 2000 Mar 3;86(4):386-90
references.pmid: 10700442
references.citation: J Physiol. 1998 Nov 15;513 ( Pt 1):171-83
references.pmid: 9782168
references.citation: J Biol Chem. 2009 Nov 6;284(45):30889-96
references.pmid: 19736309
references.citation: Am J Physiol Heart Circ Physiol. 2009 Jul;297(1):H247-56
references.pmid: 19395549
references.citation: Am J Physiol Heart Circ Physiol. 2005 Aug;289(2):H801-12
references.pmid: 15792987
references.citation: Circ Res. 1998 Sep 21;83(6):602-7
references.pmid: 9742055
references.citation: J Physiol. 2007 Feb 15;579(Pt 1):161-73
references.pmid: 17138609
references.citation: J Gen Physiol. 2010 Aug;136(2):159-77
references.pmid: 20660660
references.citation: Am J Physiol Regul Integr Comp Physiol. 2007 Oct;293(4):R1595-607
references.pmid: 17626127
references.citation: Biophys J. 2006 Apr 15;90(8):2867-76
references.pmid: 16443664
references.citation: J Physiol. 2013 Mar 1;591(5):1217-34
references.pmid: 23207592
references.citation: Biophys J. 2000 Jun;78(6):3120-37
references.pmid: 10827989
references.citation: J Mol Cell Cardiol. 2012 Oct;53(4):542-51
references.pmid: 22884844
references.citation: J Physiol (Paris). 1979;75(5):463-505
references.pmid: 533865
references.citation: Am J Physiol Heart Circ Physiol. 2001 Apr;280(4):H1814-20
references.pmid: 11247796
references.citation: Arch Biochem Biophys. 2012 Sep 1;525(1):1-8
references.pmid: 22684024
references.citation: FASEB J. 2013 Sep;27(9):3848-59
references.pmid: 23748972
references.citation: J Mol Cell Cardiol. 2010 May;48(5):979-88
references.pmid: 20004663
references.citation: Circ Res. 1995 May;76(5):734-41
references.pmid: 7728989
references.citation: J Gen Physiol. 2001 Feb;117(2):133-48
references.pmid: 11158166
references.citation: Arch Biochem Biophys. 2013 Jul 1;535(1):3-13
references.pmid: 23111184
references.citation: Am J Physiol Heart Circ Physiol. 2000 Feb;278(2):H412-9
references.pmid: 10666070
references.citation: Proc Natl Acad Sci U S A. 1986 May;83(10):3542-6
references.pmid: 2939452
references.citation: Arch Biochem Biophys. 2013 Jul 1;535(1):14-21
references.pmid: 23274408
references.citation: Physiol Rev. 2000 Apr;80(2):853-924
references.pmid: 10747208
references.citation: Biophys J. 2012 Sep 5;103(5):940-8
references.pmid: 23009843
references.citation: J Biol Chem. 1984 Oct 25;259(20):12628-32
references.pmid: 6490635
references.citation: J Physiol. 2006 Jul 1;574(Pt 1):263-73
references.pmid: 16644804
references.citation: Proc Natl Acad Sci U S A. 2002 Apr 30;99(9):6252-6
references.pmid: 11972044
references.citation: Circ Res. 2009 Dec 4;105(12):1232-9
references.pmid: 19850940
references.citation: Biochemistry. 2009 Aug 18;48(32):7722-31
references.pmid: 19586048
references.citation: J Physiol. 2009 Oct 15;587(Pt 20):4873-86
references.pmid: 19736304
references.citation: Circ Res. 1999 Jun 11;84(11):1310-7
references.pmid: 10364569
references.citation: Am J Physiol Heart Circ Physiol. 2001 Sep;281(3):H1217-22
references.pmid: 11514290
references.citation: J Clin Invest. 1998 Jun 15;101(12):2800-11
references.pmid: 9637714