20% and 30% α MHC increased dF/dtmax by 186% and 280%,respectively. These results suggest that low-levels of α MHCmay have a profound effect on systolic ejection.

Keywords: Myosin heavy chain; Cardiac function; MyofibrillarATPase

doi:10.1016/j.yjmcc.2007.03.241

Actomyosin interactions in cMYBP-C−/− miceY. Lecarpentier1,2, N. Vignier3, P. Oliviero2, A. Guellich2, M.Cortès-Morichetti1, L. Carrier3,4, C. Coirault2. 1AP-HP, Paris,France. 2Inserm U689, Paris, France. 3U582, Paris, France.4Institute of Pharmacology, UKE, Hamburg, Germany

The precise role of cardiac myosin binding protein C(cMyBP-C) on contractility and on actomyosin interaction(AMI) remains unknown. We hypothesized that the lack ofcMyBP-C impaired cardiac AMI. Mechanical properties andAMI characteristics in left papillary muscle and the in vitromotility of actin filaments on purified myosin molecules wereperformed from 16-weeks old cMyBP-C−/−KO and WT (n=16in both groups). Compared to WT, both total tension and maxi-mum shortening velocity were lower in KO (p<0.001). Theprobability of cross-bridge attachment was higher in KO than inWT (8.6±0.3 vs. 5.4±0.2%, p<0.05). The number of activeAIM was lower in KO (6.4±0.9 vs. 11.6±1.0 109/mm2, p<0.001) as well as the unitary force per AIM (p<0.01). Powerstroke probability was reduced in KO compared to WT (5.0±0.4 vs. 8.1±0.4%, p<0.05). Myosin-based velocities of actinwere slower in KO than in WT (1.65±0.01 vs. 1.98±0.01 μm/s,p<0.01). These data suggest that cMyBP-C regulates AIM bylimiting inefficient cross-bridge formation and by enhancing thepower stroke step.

Keywords: Energetics; Contractile proteins; Cardiac function

doi:10.1016/j.yjmcc.2007.03.242

Contribution of ATP synthase to stimulation of respirationby Ca2+ in heart mitochondriaRasa Baniene1,2, Zita Nauciene1,3, Vida Mildaziene3. 1Institutefor Biomed. Research, Kaunas University of Medicine.2Department of Biochemistry, Kaunas University of Medicine,Kaunas, Lithuania. 3Vytautas Magnus University, Kaunas,Lithuania

A variety of experimental conditions was applied with theaim to estimate the correlation between the contribution of ATPsynthase to the respiratory flux control and calcium inducedactivation of succinate oxidation in heart mitochondria isolatedfrom rat, rabbit and guinea-pig. The sensitivity of respiration inheart mitochondria to the decrease in temperature from 37 °C to

28 °C decreases in the row rabbit>guinea-pig> rat. Ca2+ effecton succinate oxidation rate in state 3 respiration was species andtemperature dependent and ranged from zero (rat, 37 °C) to+44% (rabbit, 28 °C). For mitochondria from all experimentalanimals the increase of Ca2+ in physiological range of concen-tration did not change state 2 respiration rate, and the stimu-latory effect of Ca2+ on state 3 respiration was more pronouncedat 28 °C than at 37 °C. The respiratory subsystem was sensitiveto Ca2+ ions only in rabbit heart mitochondria. A high positivecorrelation between Ca2+ ability to stimulate succinate oxida-tion in state 3 and the control exerted by ATP synthase over therespiratory flux provides argument confirming stimulation ofATP synthase by Ca2+ ions.

Keywords: Heart mitochondria; Calcium; ATP synthase

doi:10.1016/j.yjmcc.2007.03.243

In vivo degradation of nitric-oxide synthase isozymes bycalpain is regulated by HSP90E. Melloni, M. Averna, R. Stifanese, R. De Tullio, F. Salamino,S. Pontremoli. DIMES, University of Genoa, Viale BenedettoXV, 1-16132 Genoa, Italy

The occurrence of a proteolytic degradation of NOS isozymesin conditions of altered intracellular free [Ca2+] has been studied“in vivo” using as animal models normotensive and geneticallyhypertensive rats treated with a high sodium diet. A strictcorrelation between degradation of NOS active forms and ele-vation of [Ca2+]i was established. In aorta, eNOS was exten-sively degraded, without the accumulation of active fragments,this leading to a net loss of both protein and activity, whereas inbrain, nNOS cleavage produced the accumulation of still activelow Mr synthase forms, this preventing a significant loss ofcatalytic activity. Identical digestion patterns were obtained inCa2+ loaded cells or in reconstructed systems in which purifiedNOS isozymes were exposed to purified calpain. Preincubationwith synthetic calpain inhibitor prevented such degradation.

Moreover, HSP90 protects from degradation both eNOS andnNOS isozymes. However, the intensive degradation of eNOS inaorta, compared to the conservative proteolysis of nNOSobserved in brain, can be ascribed to a different levels ofHSP90, found to be present in large excess in nervous tissue andin lower amounts in aorta. In this tissue calpain activation isfurther enhanced by an extensive degradation of calpastatin,which favours the digestion of also HSP90, in addition to eNOS.

The “in vivo” calpain mediated degradation of eNOS andHSP90 observed in aorta may be part of a process leading toirreversible cell damages, promoted by a prolonged alteration ofCa2+ homeostasis.

Keywords: Calcium; Endothelial NO synthase; Hypertension

doi:10.1016/j.yjmcc.2007.03.244

S108 ABSTRACTS / Journal of Molecular and Cellular Cardiology 42 (2007) S102–S124