Alterations in Thin Filament Regulation Induced by a Human Cardiac Troponin T Mutant That Causes Dilated Cardiomyopathy Are Distinct from Those Induced by Troponin T Mutants That Cause Hypertrophic Cardiomyopathy

We have compared the in vitroregulatory properties of recombinant human cardiac troponin reconstituted using wild type troponin T with troponin containing the ΔLys-210 troponin T mutant that causes dilated cardiomyopathy (DCM) and the R92Q troponin T known to cause hypertrophic cardiomyopathy (HCM). Troponin containing ΔLys-210 troponin T inhibited actin-tropomyosin-activated myosin subfragment-1 ATPase activity to the same extent as wild type at pCa8.5 (>80%) but produced substantially less enhancement of ATPase atpCa4.5. The Ca2+ sensitivity of ATPase activation was increased (ΔpCa50 = +0.2pCa units) and cooperativity of Ca2+ activation was virtually abolished. Equimolar mixtures of wild type and ΔLys-210 troponin T gave a lower Ca2+ sensitivity than with wild type, while maintaining the diminished ATPase activation atpCa4.5 observed with 100% mutant. In contrast, R92Q troponin gave reduced inhibition at pCa8.5 but greater activation than wild type at pCa4.5; Ca2+sensitivity was increased but there was no change in cooperativity.In vitro motility assay of reconstituted thin filaments confirmed the ATPase results and moreover indicated that the predominant effect of the ΔLys-210 mutation was a reduced sliding speed. The functional consequences of this DCM mutation are qualitatively different from the R92Q or any other studied HCM troponin T mutation, suggesting that DCM and HCM may be triggered by distinct primary stimuli. We have compared the in vitroregulatory properties of recombinant human cardiac troponin reconstituted using wild type troponin T with troponin containing the ΔLys-210 troponin T mutant that causes dilated cardiomyopathy (DCM) and the R92Q troponin T known to cause hypertrophic cardiomyopathy (HCM). Troponin containing ΔLys-210 troponin T inhibited actin-tropomyosin-activated myosin subfragment-1 ATPase activity to the same extent as wild type at pCa8.5 (>80%) but produced substantially less enhancement of ATPase atpCa4.5. The Ca2+ sensitivity of ATPase activation was increased (ΔpCa50 = +0.2pCa units) and cooperativity of Ca2+ activation was virtually abolished. Equimolar mixtures of wild type and ΔLys-210 troponin T gave a lower Ca2+ sensitivity than with wild type, while maintaining the diminished ATPase activation atpCa4.5 observed with 100% mutant. In contrast, R92Q troponin gave reduced inhibition at pCa8.5 but greater activation than wild type at pCa4.5; Ca2+sensitivity was increased but there was no change in cooperativity.In vitro motility assay of reconstituted thin filaments confirmed the ATPase results and moreover indicated that the predominant effect of the ΔLys-210 mutation was a reduced sliding speed. The functional consequences of this DCM mutation are qualitatively different from the R92Q or any other studied HCM troponin T mutation, suggesting that DCM and HCM may be triggered by distinct primary stimuli. Dilated cardiomyopathy (DCM) 1The abbreviations used are: DCM, dilated cardiomyopathy; HCM, hypertrophic cardiomyopathy; S-1, subfragment 1; PIPES, 1,4-piperazinediethanesulfonic acid; HMM, heavy meromyosin. 1The abbreviations used are: DCM, dilated cardiomyopathy; HCM, hypertrophic cardiomyopathy; S-1, subfragment 1; PIPES, 1,4-piperazinediethanesulfonic acid; HMM, heavy meromyosin. is defined clinically by cardiac chamber dilatation with reduced contractile performance in the absence of underlying coronary artery disease. The heart appears thin walled and distended and, at the microscopic level, there is moderate myocyte hypertrophy and death, along with replacement fibrosis. Echocardiographic screening of relatives of affected individuals suggests that ∼25–35% of cases are familial (1Keeling P.J. Gang Y. Smith G. Seo H. Bent S.E. Murday V. Caforio A.L. McKenna W.J. Br. Heart J. 1995; 73: 417-421Google Scholar, 2Michels V.V. Moll P.P. Miller F.A. Tajik A.J. Chu J.S. Driscoll D.J. Burnett J.C. Rodeheffer R.J. Chesebro J.H. Tazelaar H.D. N. Engl. J. Med. 1992; 326: 77-82Google Scholar). The disease is frequently inherited with an associated phenotype such as conduction disease, skeletal myopathy, or sensorineural hearing loss. To date, as many as 18 loci that cause DCM as the predominant phenotype have been identified, and in all but two of these, the disease is inherited in an autosomal dominant manner (3Seidman J.G. Seidman C. Cell. 2001; 104: 557-567Google Scholar, 4Schonberger J. Seidman C.E. Am. J. Hum. Genet. 2001; 69: 249-260Google Scholar). For 10 of the loci, the disease genes have been identified. These encode a diverse range of proteins, including components of the sarcomere: actin (ACTC) (5Olson T.M. Michels V.V. Thibodeau S.N. Tai Y.S. Keating M.T. Science. 1998; 280: 750-752Google Scholar); β-myosin heavy chain (MYH7) (6Kamisago M. Sharma S.D. DePalma S.R. Solomon S. Sharma P. McDonough B. Smoot L. Mullen M.P. Woolf P.K. Wigle E.D. Seidman J.G. Seidman C.E. Jarcho J. Shapiro L.R. N. Engl. J. Med. 2000; 343: 1688-1696Google Scholar); titin (TTN) (7Gerull B. Gramlich M. Atherton J. McNabb M. Trombitas K. Sasse-Klaassen S. Seidman J.G. Seidman C. Granzier H. Labeit S. Frenneaux M. Thierfelder L. Nat. Genet. 2002; 30: 201-204Google Scholar); α-tropomyosin (TPM1) (8Olson T.M. Kishimoto N.Y. Whitby F.G. Michels V.V. J. Mol. Cell Cardiol. 2001; 33: 723-732Google Scholar); and cardiac troponin T (TNNT2) (6Kamisago M. Sharma S.D. DePalma S.R. Solomon S. Sharma P. McDonough B. Smoot L. Mullen M.P. Woolf P.K. Wigle E.D. Seidman J.G. Seidman C.E. Jarcho J. Shapiro L.R. N. Engl. J. Med. 2000; 343: 1688-1696Google Scholar). In a recent report, Kamisago et al. (6Kamisago M. Sharma S.D. DePalma S.R. Solomon S. Sharma P. McDonough B. Smoot L. Mullen M.P. Woolf P.K. Wigle E.D. Seidman J.G. Seidman C.E. Jarcho J. Shapiro L.R. N. Engl. J. Med. 2000; 343: 1688-1696Google Scholar) identified two mutations in β-myosin heavy chain and one in cardiac troponin T (the deletion of lysine 210) in kindreds having autosomal dominant dilated cardiomyopathy without conduction disease, skeletal muscle dysfunction, or other accompanying phenotypes. It was noteworthy that affected subjects did not have ventricular hypertrophy, and histology from one subject showed mildly increased interstitial fibrosis without the myocyte and myofibrillar disarray characteristic of hypertrophic cardiomyopathy (HCM). These mutations therefore appear to cause dilated cardiomyopathy directly and induce a phenotype that is distinctly different from HCM. HCM is known to be caused by mutations in at least 10 genes, all but one of which encodes a sarcomeric protein (3Seidman J.G. Seidman C. Cell. 2001; 104: 557-567Google Scholar, 9Blair E. Redwood C. Ashrafian H. Oliveira M. Broxholme J. Kerr B. Salmon A. Ostman-Smith I. Watkins H. Hum. Mol. Genet. 2001; 10: 1215-1220Google Scholar). In contrast to the contractile protein gene mutations that cause DCM, the functional consequences of the HCM mutations have been extensively characterized (reviewed in Refs. 3Seidman J.G. Seidman C. Cell. 2001; 104: 557-567Google Scholar, 10Redwood C.S. Moolman-Smook J.C. Watkins H. Cardiovasc. Res. 1999; 44: 20-36Google Scholar, and 11Hernandez O.M. Housmans P.R. Potter J.D. J. Appl. Physiol. 2001; 90: 1125-1136Google Scholar). Most mutations in sarcomeric proteins have been found to increase maximum shortening speed and/or Ca2+ sensitivity in vitro, which may result in energetic compromise through increased cost of force productionin vivo (9Blair E. Redwood C. Ashrafian H. Oliveira M. Broxholme J. Kerr B. Salmon A. Ostman-Smith I. Watkins H. Hum. Mol. Genet. 2001; 10: 1215-1220Google Scholar, 12Sweeney H.L. Feng H.S. Yang Z. Watkins H. Proc. Natl. Acad. Sci. U. S. A. 1998; 95: 14406-14410Google Scholar, 13Montgomery D.E. Tardiff J.C. Chandra M. J. Physiol. (Lond.). 2001; 536: 583-592Google Scholar, 14Franz W.M. Muller O.J. Katus H.A. Lancet. 2001; 358: 1627-1637Google Scholar, 15Watkins H. Eur. Heart J. 2001; 3 (suppl.): L43-L50Google Scholar). In HCM families, some individuals go on to develop a dilated cardiomyopathy phenotype, presumably through induction of apoptosis (3Seidman J.G. Seidman C. Cell. 2001; 104: 557-567Google Scholar). Thus, one plausible hypothesis to explain how different mutations in the same gene can cause different cardiomyopathies is that DCM mutations produce similar, but more severe, perturbations of contractile protein function, sufficient to result in cell death. Alternatively, the DCM mutations in sarcomeric protein genes could initiate disease through qualitatively different perturbations of contractility (6Kamisago M. Sharma S.D. DePalma S.R. Solomon S. Sharma P. McDonough B. Smoot L. Mullen M.P. Woolf P.K. Wigle E.D. Seidman J.G. Seidman C.E. Jarcho J. Shapiro L.R. N. Engl. J. Med. 2000; 343: 1688-1696Google Scholar, 16Marston S.B. Hodgkinson J.L. J. Muscle Res. Cell Motil. 2001; 22: 1-4Google Scholar). Functional analysis of different mutations within a single gene that produce the divergent phenotypes of HCM and DCM provides a valuable opportunity to investigate the triggers that discriminate between these two disease pathways. In this report, we have focused on the ΔLys-210 troponin T mutant that causes DCM. In common with the HCM troponin T mutations, it is highly likely that this apparently subtle mutation acts in a dominant-negative manner and is incorporated into the thin filament, where it affects normal thin filament function. The deleted amino acid forms one of a stretch of four lysine residues in human cardiac troponin T (amino acids 207–210). These lie within the globular C-terminal T2 domain (residues 188–288) which binds to troponins I and C as well as to tropomyosin (17Perry S.V. J. Muscle Res. Cell Motil. 1998; 19: 575-602Google Scholar) and may therefore affect thin filament function by a variety of mechanisms. We have compared the changes in thin filament function caused by the ΔLys-210 mutation with those caused by a mutation in troponin T that causes HCM. For the latter we have used the R92Q troponin T mutant, which has been extensively characterized in transgenic mouse models (13Montgomery D.E. Tardiff J.C. Chandra M. J. Physiol. (Lond.). 2001; 536: 583-592Google Scholar, 18Oberst L. Zhao G. Park J.T. Brugada R. Michael L.H. Entman M.L. Roberts R. Marian A.J. J. Clin. Invest. 1998; 102: 1498-1505Google Scholar, 19Tardiff J.C. Hewett T.E. Palmer B.M. Olsson C. Factor S.M. Moore R.L. Robbins J. Leinwand L.A. J. Clin. Invest. 1999; 104: 469-481Google Scholar) and myofibrils (20Morimoto S. Yanaga F. Minakami R. Ohtsuki I. Am. J. Physiol. 1998; 275: C200-C207Google Scholar,21Szczesna D. Zhang R. Zhao J. Jones M. Guzman G. Potter J.D. J. Biol. Chem. 2000; 275: 624-630Google Scholar) 2R. Willott and C. Ashley, unpublished data. 2R. Willott and C. Ashley, unpublished data. but has not yet been examined in reconstituted thin filaments in vitro. We found that the ΔLys-210 mutation had distinctive effects upon thin filament function: the maximally activated ATPase activity and filament sliding speed were decreased, and Ca2+ activation became non-cooperative. This pattern of changes was quite unlike the effect of the R92Q HCM mutation (increased ATPase activity and sliding speed and higher Ca2+ sensitivity with unaltered cooperativity) but closely resembled the properties of troponin extracted from end stage failing human hearts studied by the same techniques (22Purcell I.F. Bing W. Marston S.B. Cardiovasc. Res. 1999; 43: 884-891Google Scholar, 23Knott A. Purcell I.F. Marston S.B. J. Mol. Cell. Cardiol. 2002; 34: 469-482Google Scholar). Rabbit skeletal muscle actin, rabbit and human cardiac muscle α-tropomyosin, and subfragment-1 (S-1) derived by chymotryptic digestion of whole rabbit skeletal muscle myosin were prepared as previously described (22Purcell I.F. Bing W. Marston S.B. Cardiovasc. Res. 1999; 43: 884-891Google Scholar, 24Redwood C.S. Lohmann K. Bing W. Esposito G.M. Elliott K. Abdulrazzak H. Knott A. Purcell I. Marston S.B. Watkins H. Circ. Res. 2000; 86: 1146-1152Google Scholar). Recombinant wild type human troponin subunits were overexpressed in BL21(DE3)pLysS Escherichia coli and subsequently purified (24Redwood C.S. Lohmann K. Bing W. Esposito G.M. Elliott K. Abdulrazzak H. Knott A. Purcell I. Marston S.B. Watkins H. Circ. Res. 2000; 86: 1146-1152Google Scholar). pMW172 expression constructs encoding R92Q and ΔLys-210 troponin T were made, respectively, by subcloning from an existing plasmid H.L. Feng H.S. Yang Z. Watkins H. Proc. Natl. Acad. Sci. U. S. A. 1998; 95: 14406-14410Google Scholar) and using a troponin were using a of K. Watkins H. Redwood C.S. J. Biol. Chem. 2000; 275: Scholar). The subunits were in a of troponin troponin troponin T in 10 and the of and were reduced using a to and The mixtures were to and troponin purified by using a were into the assay The of subunits were by and found to be = wild type and were as previously described using myosin and thin filaments reconstituted using and troponin or actin, and troponin in PIPES, at K. Watkins H. Redwood C.S. J. Biol. Chem. 2000; 275: Scholar). The Ca2+ was using and the of as previously described K. Watkins H. Redwood C.S. J. Biol. Chem. 2000; 275: Scholar). The of thin filaments a of skeletal muscle heavy was using the in vitro motility assay as we have described (24Redwood C.S. Lohmann K. Bing W. Esposito G.M. Elliott K. Abdulrazzak H. Knott A. Purcell I. Marston S.B. Watkins H. Circ. Res. 2000; 86: 1146-1152Google Scholar, W. Marston S.B. J. Scholar). was with as described by et al. Scholar). at was in to a of on the The was by in and reconstituted thin filaments were were at with the of reconstituted thin filament 10 rabbit skeletal actin, human cardiac reconstituted human cardiac troponin in 3 troponin at assay tropomyosin and troponin were to The of actin tropomyosin filaments the skeletal muscle was observed a were in cell any had were and the was to of filaments and of filaments using the described by Marston et al. S.B. Bing W. G. J. Muscle Res. Cell Motil. Scholar). Troponin were reconstituted from recombinant human cardiac troponins and T using wild type troponin ΔLys-210 mutant troponin or R92Q mutant troponin filaments were using rabbit skeletal actin, rabbit or human α-tropomyosin, and wild type or mutant The functional properties of wild type and mutant troponin T were compared by assay of thin filament activation of skeletal muscle myosin ATPase activity and by vitro motility assay using skeletal muscle heavy meromyosin. as previously described K. Watkins H. Redwood C.S. J. Biol. Chem. 2000; 275: Scholar) showed that the of the wild type and mutant troponins to were not In ATPase the of wild type troponin increased ATPase a at of the ATPase using troponin containing ΔLys-210 troponin T was the maximum ATPase activation was of the This was in four different troponin and was highly troponin increased the speed of filament sliding in the in vitro motility a at troponin previously observed (24Redwood C.S. Lohmann K. Bing W. Esposito G.M. Elliott K. Abdulrazzak H. Knott A. Purcell I. Marston S.B. Watkins H. Circ. Res. 2000; 86: 1146-1152Google Scholar, wild type troponin increased sliding to that of filaments reconstituted with troponin containing ΔLys-210 troponin T gave a reduced sliding speed of and this was highly Troponin containing ΔLys-210 mutant troponin T a but in the of filaments compared with wild type troponin C and of the reconstituted thin filaments showed that wild type and mutant thin filaments a of troponin subunits and tropomyosin ATPase activation and filament motility of thin filaments containing wild type and ΔLys-210 mutant troponin T were ATPase activity was inhibited by and in vitro motility was by troponin such that of the filaments were and the speed of the filaments was than in with (24Redwood C.S. Lohmann K. Bing W. Esposito G.M. Elliott K. Abdulrazzak H. Knott A. Purcell I. Marston S.B. Watkins H. Circ. Res. 2000; 86: 1146-1152Google Scholar, D. Abdulrazzak H. Knott A. Elliott K. Redwood C. Watkins H. Marston S. C. J. 2002; Scholar) using this The maximum of motility troponin with wild type and ΔLys-210 mutant troponin from of thin we found no in the of filaments at troponin at These results that the of inhibition caused by troponin containing ΔLys-210 mutant troponin the maximum inhibition of was different from wild filaments reconstituted with troponin containing the HCM troponin T mutation R92Q gave activation of ATPase activity of activity compared with using wild and thin filament sliding and In thin filaments containing R92Q troponin T gave less inhibition of ATPase compared with using wild type and less inhibition of filament motility than wild type = We the Ca2+ of thin filament activation of ATPase activity and motility using of troponin that gave inhibition of filament activity at motility pattern of results was with the ATPase of filaments and filament of thin filaments containing ΔLys-210 mutant troponin T were less less than those using wild type and activation was to lower The were to the = a The ΔLys-210 mutation increased and of filaments and sliding The derived from of the mutant troponin were to = and and the ATPase were well by a with = that these thin filaments were not activated by In contrast, the R92Q troponin T mutation had a different the Ca2+ sensitivity of ATPase was increased with no change in cooperativity and the Ca2+ activation of thin filaments containing wild type and mutant type troponin = = = = = troponin = = = = = troponin = were at and motility was at from were to the and the S.E. of the derived and are in the in a ATPase were at and motility was at from were to the and the S.E. of the derived and are in the The disease caused by the DCM and HCM troponin T mutations is autosomal and it is likely that the cardiac thin filaments of affected individuals of wild type and mutant has that the effect on thin filament function of mixtures of wild type and mutant troponin is not directly from the functional properties of the mutant troponin (24Redwood C.S. Lohmann K. Bing W. Esposito G.M. Elliott K. Abdulrazzak H. Knott A. Purcell I. Marston S.B. Watkins H. Circ. Res. 2000; 86: 1146-1152Google Scholar, K. Watkins H. Redwood C.S. J. Biol. Chem. 2000; 275: Scholar). filaments were reconstituted using of actin, and troponin wild type, mutant, or wild type containing an of wild type and mutant gave activation to at that was to the using 100% mutant and less than that with wild type troponin in vitro motility assay the speed of sliding of a was to that of 100% mutant 100% mutant, and 100% wild type, In contrast, thin filaments reconstituted with an of wild type troponin T and R92Q mutant troponin T gave of activation and inhibition as 100% wild type 100% ΔLys-210 troponin T mutant gave an increase in Ca2+ sensitivity of ATPase activation of the type in a in Ca2+ sensitivity compared with wild = = The the was between 100% wild type and 100% mutant and was different from that with wild type troponin The same pattern of results was observed using in vitro motility in thin filaments with a of wild type and ΔLys-210 the Ca2+ sensitivity of the was less than wild type by not containing an of wild type and R92Q troponin T produced an increase in the Ca2+ sensitivity of of ATPase activation that was between wild type and mutant filaments with no change in cooperativity (ΔpCa50 = wild compared with = The deletion of lysine in cardiac troponin T has been to be a cause of inherited dilated cardiomyopathy (6Kamisago M. Sharma S.D. DePalma S.R. Solomon S. Sharma P. McDonough B. Smoot L. Mullen M.P. Woolf P.K. Wigle E.D. Seidman J.G. Seidman C.E. Jarcho J. Shapiro L.R. N. Engl. J. Med. 2000; 343: 1688-1696Google Scholar). human cardiac troponin T with this mutation was incorporated into reconstituted thin we found a pattern of functional vitro that was distinctly different from the changes previously observed with hypertrophic cardiomyopathy The of and the thin filament sliding speed were reduced compared with wild type the Ca2+ activation became and was It is noteworthy that a of wild type and mutant troponin which is likely to the in reduced the maximally activated ATPase and filament sliding speed to the same as 100% mutant troponin T but gave Ca2+ sensitivity lower than wild The deleted amino acid forms one of a stretch of four lysine residues in human cardiac troponin T (amino acids 207–210). These amino acids lie within the C-terminal chymotryptic T2 known to troponin and troponin I (17Perry S.V. J. Muscle Res. Cell Motil. 1998; 19: 575-602Google Scholar). of and within this have indicated that troponin I binds to C-terminal to these four residues R. P.K. S. Proc. Natl. Acad. Sci. U. S. A. 1998; 95: troponin C and tropomyosin may to or directly with these residues 1999; Scholar). The S. A. K. Y. J. 2002; Scholar) of the T2 in with troponins I and C that forms of a to the in a with troponin I that has no with any other troponin The change in maximum sliding speed and ATPase is with that have that one function of troponin T is to the H.L. Feng H.S. Yang Z. Watkins H. Proc. Natl. Acad. Sci. U. S. A. 1998; 95: 14406-14410Google Scholar, W. Marston S.B. J. Scholar, J.D. Z. Zhao J. J. Biol. Chem. 1995; Scholar); the of activation could be to the of troponin T in the of the thin filament through with tropomyosin J. Scholar, S. 1995; 34: Scholar). The recent of a DCM mutation within the domain of troponin which binds to tropomyosin D. A. Brugada R. R. J.L. M. Roberts R. 2001; 104: and two mutations in tropomyosin (8Olson T.M. Kishimoto N.Y. Whitby F.G. Michels V.V. J. Mol. Cell Cardiol. 2001; 33: 723-732Google Scholar) that in T may be the of the DCM phenotype (reviewed in 16Marston S.B. Hodgkinson J.L. J. Muscle Res. Cell Motil. 2001; 22: 1-4Google Scholar). The Ca2+ sensitivity observed with wild mixtures was the increase in Ca2+ sensitivity in using 100% DCM mutant troponin This that the properties of a wild troponin are quite different from wild type and mutant troponin in a that could not be from the functional properties of the mutant troponin (24Redwood C.S. Lohmann K. Bing W. Esposito G.M. Elliott K. Abdulrazzak H. Knott A. Purcell I. Marston S.B. Watkins H. Circ. Res. 2000; 86: 1146-1152Google Scholar, K. Watkins H. Redwood C.S. J. Biol. Chem. 2000; 275: Scholar, D. Abdulrazzak H. Knott A. Elliott K. Redwood C. Watkins H. Marston S. C. J. 2002; Scholar). The of has a Ca2+ sensitivity in rabbit heart in which troponin was upon with human troponin T wild type or and human reconstituted in by the of human troponins I and C K. F. Minakami R. M. Ohtsuki I. Proc. Natl. Acad. Sci. U. S. A. 2002; Scholar). It appears that these human mutant troponin T and rabbit troponin Ca2+ sensitivity with the and reduced cooperativity that the expression and of this DCM troponin T vivo may result in that are less to more and are to produce sufficient force the changes in contractility to be caused by the DCM troponin T mutant closely the in identified in end stage failing human using from hearts affected by a of have a pattern of reduced shortening speed and reduced myofibrillar ATPase activity R.J. W. Res. Cardiol. 1992; Scholar, H. J. H. F. H. C. Cardiovasc. Res. 1998; Scholar, P.P. Cardiovasc. Res. 1998; Scholar). are less changes in Ca2+ sensitivity that has been to be increased or recent suggests that such as and are in which the Ca2+ sensitivity change M.L. J. Clin. Invest. Scholar, R.J. U. C.S. D. 2000; Scholar, J. R. W. L. 2001; 104: Scholar). The reduced shortening speed with the reduced ATPase and sliding speed caused by the ΔLys-210 mutation in troponin The effects of the ΔLys-210 mutation with the properties of troponin extracted from failing heart troponin was found to a maximum sliding speed and a higher Ca2+ sensitivity with reduced cooperativity (22Purcell I.F. Bing W. Marston S.B. Cardiovasc. Res. 1999; 43: 884-891Google Scholar, 23Knott A. Purcell I.F. Marston S.B. J. Mol. Cell. Cardiol. 2002; 34: 469-482Google Scholar). it is that a reduced maximum of is a common of end stage heart a of this could not be by Ca2+ sensitivity or Ca2+ K. S. E. 1999; Scholar). It these contractility changes in end stage failing hearts the of heart or are the that a troponin T mutant that is inherited DCM changes in contractility the that to troponin may directly to the of forms of DCM. The functional caused by the ΔLys-210 troponin T mutation are in many from the the R92Q HCM mutant and from of other HCM troponin T 24Redwood C.S. Lohmann K. Bing W. Esposito G.M. Elliott K. Abdulrazzak H. Knott A. Purcell I. Marston S.B. Watkins H. Circ. Res. 2000; 86: 1146-1152Google Scholar). H. and C. unpublished data. this of properties is distinct from any other in vitro on HCM troponin T D. Zhang R. Zhao J. Jones M. Guzman G. Potter J.D. J. Biol. Chem. 2000; 275: 624-630Google Scholar, D. C. C. N. D. E. J. Biol. Chem. 1999; Scholar, Potter J.D. Cardiovasc. Med. 2001; suggesting that the reduced and, at an with wild type diminished Ca2+ sensitivity may a the of the than We Ashley, and Smith on these data.