Lys184 deletion in troponin I impairs relaxation kinetics and induces hypercontractility in murine cardiac myofibrils.
OBJECTIVE
To understand the functional consequences of the Lys184 deletion in murine cardiac troponin I (mcTnI(DeltaK184)), we have studied the primary effects of this mutation linked to familial hypertrophic cardiomyopathy (FHC) at the sarcomeric level.


RESULTS
Ca(2+) sensitivity and kinetics of force development and relaxation were investigated in cardiac myofibrils from transgenic mice expressing mcTnI(DeltaK184), as a model which co-segregates with FHC. Ca(2+)-dependent conformational changes (switch-on/off) of the fluorescence-labelled human troponin complex, containing either wild-type hcTnI or mutant hcTnI(DeltaK183), were investigated in myofibrils prepared from the guinea pig left ventricle. Ca(2+) sensitivity and maximum Ca(2+)-activated and passive forces were significantly enhanced and cooperativity was reduced in mutant myofibrils. At partial Ca(2+) activation, mutant but not wild-type myofibrils displayed spontaneous oscillatory contraction of sarcomeres. Both conformational switch-off rates of the incorporated troponin complex and the myofibrillar relaxation kinetics were slowed down by the mutation. Impaired relaxation kinetics and increased force at low [Ca(2+)] were reversed by 2,3-butanedione monoxime (BDM), which traps cross-bridges in non-force-generating states.


CONCLUSIONS
We conclude that these changes are not due to alterations of the intrinsic cross-bridge kinetics. The molecular mechanism of sarcomeric diastolic dysfunction in this FHC model is based on the impaired regulatory switch-off kinetics of cTnI, which induces incomplete inhibition of force-generating cross-bridges at low [Ca(2+)] and thereby slows down relaxation of sarcomeres. Ca(2+) sensitization and impairment of the relaxation of sarcomeres induced by this mutation may underlie the enhanced systolic function and diastolic dysfunction at the sarcomeric level.
Iorga
Bogdan
B
Institute of Vegetative Physiology, University of Cologne, Robert-Koch-Strasse 39, Cologne, Germany. bogdan.iorga@uni-koeln.de
Blaudeck
Natascha
N
Solzin
Johannes
J
Neulen
Axel
A
Stehle
Ina
I
Lopez Davila
Alfredo J
AJ
Pfitzer
Gabriele
G
Stehle
Robert
R
D000818:Animals; D020013:Calcium Signaling; D024741:Cardiomyopathy, Hypertrophic, Familial / Q000235:genetics / Q000378:metabolism* / Q000503:physiopathology; D003931:Diacetyl / Q000031:analogs & derivatives / Q000494:pharmacology; D004195:Disease Models, Animal; D006168:Guinea Pigs; D006801:Humans; D007700:Kinetics; D008239:Lysine; D051379:Mice; D008810:Mice, Inbred C57BL; D008822:Mice, Transgenic; D009119:Muscle Contraction / Q000187:drug effects; D053580:Muscle Strength; D009210:Myofibrils / Q000378:metabolism* / Q000473:pathology; D010210:Papillary Muscles / Q000187:drug effects / Q000378:metabolism* / Q000473:pathology / Q000503:physiopathology; D011487:Protein Conformation; D012518:Sarcomeres / Q000378:metabolism; D017384:Sequence Deletion; D019210:Troponin I / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D018487:Ventricular Dysfunction, Left / Q000235:genetics / Q000378:metabolism* / Q000503:physiopathology
D019210:Troponin I; C004717:diacetylmonoxime; D003931:Diacetyl; D008239:Lysine