microscopy. T-tubular ErbB2 co-localized with Cav3 in the F1Bgroup and not in the TO2 DCM group. ErbB2 co-localized withDys in the TO2 DCM group and not in the F1B group. T-tubularco-localization of ErbB2 and βDG was observed in the F1Bgroup. Co-immunoprecipitation demonstrated: (1) An associa-tion of ErbB2 and βDG in the F1B group that was decreased inthe TO2 DCM group and (2) an association of ErbB2 and Src inthe TO2 group that is decreased in the F1B group.

Conclusion: The loss of ErbB2-Cav3-βDG association andthe onset of ErbB2-Src-Dys interaction correlates with theinitiation of DCM.

Keywords: ErbB2 receptor tyrosine kinase; Dystrophinassociated protein complex; Dilated cardiomyopathy

doi:10.1016/j.yjmcc.2007.03.432

Mutations in tropomyosin that cause DCM, affectcooperativity of cardiac muscle thin filamentsS. Marston, M. Mirza, P. Robinson, E. Kremneva, D. Levitsky,C. Redwood, M. EL-Mezgueldi. Imperial College London,Cardiovascular Medicine, Oxford and Russian Academy ofSciences

E40K and E54K mutations in tropomyosin cause familialDCM. Both mutations decrease Ca2+-sensitivity. E40K alsoreduces Vmax of actin-tm-activated S-1 ATPase by 18%. Weinvestigated cooperative allosteric regulation by native tm,bacterially expressed AS-α tm and the two mutants. AS-α tmhas a lower cooperative unit size (6.5) than native a-tm (10.0).The E40K mutation reduced the size of cooperative unit to 3.7,whilst E54K had the opposite effect (n=8.0). The equilibriumbetween ON and OFF states, Kt, was the same for all actin-tmspecies; however, Kt of actin-tm-tn at pCa5 was 50% less forAS-α tm E40K than for AS-α tm and AS-α tm E54K. Kb, the‘closed’ to ‘blocked’ equilibrium constant, was the same for alltropomyosin species. The E40K mutation reduced the affinityof tropomyosin for actin by 1.74-fold, but only when in the ONstate (presence of S-1). In contrast the E54K mutation reducedaffinity by 3.5-fold only in the OFF state. Differential scanningcalorimetry measurements of AS-α Tm showed that domain 3,assigned to the N terminus of tropomyosin, was stronglydestabilised by both mutations. Additionally with AS-α tmE54K we observed a unique new domain at 55 °C accountingfor 25% of enthalpy indicating stabilisation of part oftropomyosin. The disease-causing mechanism of the E40Kmutation may be accounted for by destablisation of the ON stateof the thin filaments; however, the E54K mutation has a morecomplex effect on tropomyosin structure and function.

Keywords: Contractile proteins; Dilated cardiomyopathy;Inherited disease

doi:10.1016/j.yjmcc.2007.03.433

Influence of cTNI-R145G, related to hypertrophiccardiomyopathy, on the isotonic contraction ofcardiomyocytesStephanie Reis, Christoph Littwitz, Andreas Mügge, Lutz Pott,Kornelia Jaquet. Kardiologie, St Josef-Hospital, Gudrunstr. 56,44791 Bochum, DE

The amino acid exchange R145G in the inhibitory subunit(cTnI) of the cardiac troponin complex is related to familialhypertrophic cardiomyopathy. Troponin regulates muscle con-traction by reversible calcium binding and phosphorylationupon β-adrenergic receptor (AR) stimulation. If the response toβ-AR activation is altered due to the R145G replacement is notknown. Thus we studied the effects of cTnI-R145G on isotoniccontraction of adult cardiomyocytes with respect to β-ARstimulation. Adenovirus driven expression of human cTnI-R145G and cTnI-wild type in adult rat ventricle cells wasmonitored by co-expression of a green fluorescent protein.Incorporation into myofibrils was verified by immunofluores-cence. Sarcomere shortening, shortening and relaxation rateswere analysed using sarcomere length measurements(ISHR2006, Manchester, UK). Expression of cTnI-R145G ledto a decrease in shortening and rates of shortening andrelaxation. With isoproterenol (ISO) the negative effect onshortening was nearly compensated. Surprisingly the decreasein velocities was associated with β2-AR stimulation with orwithout Pertussis toxin. β1-AR stimulation or on addition ofForskolin, no negative effect on the kinetical parameters wasobtained. The observed effects might be evoked by factors fardownstream of the β-AR signalling pathway, e.g. by differentcalcium handling. The underlying mechanism is not known yet,but the results clearly underline that β1- and β2-AR signallingact differently on regulation of contraction.

Keywords: Cardiac hypertrophy; Cardiomyopathies;Contractile proteine

doi:10.1016/j.yjmcc.2007.03.434

Swimming induces cardiac structure change and suddendeath in mice carrying cardiac troponin I mutationDi Yang, HengFang Wu, JiZheng Ma, ShuShu Zhu, JiNanZhang. First Affiliated Hospital with Nanjing MedicalUniversity, Nanjing 210029, China

Hypertrophic cardiomyopathy (HCM) is the most commoncause of unexpected sudden cardiac death in the young.Mutations in cardiac troponin I (cTnI) gene are associatedwith HCM. Our previous finding indicated cTnI-R145W in aChinese HCM population. The present study aimed to studywhether or not exercise could affect cardiac structure andprovoke sudden death in transgenic mice carrying cTnI-R146W(in the mouse sequence). Transgenic mice were generated bymicroinjection of cardiac transgenic vector, harboring mouse a-myosin heavy chain promoter and mouse cTnI-R146W. At the

S166 ABSTRACTS / Journal of Molecular and Cellular Cardiology 42 (2007) S162–S170