Developmental changes in force-generating capacity and Ca 2+ sensitivity of contraction in murine hearts were correlated with changes in myosin heavy chain (MHC) and troponin (Tn) isoform
expression, ...using Triton-skinned fibres. The maximum Ca 2+ -activated isometric force normalized to the cross-sectional area ( F CSA ) increased mainly during embryogenesis and continued to increase at a slower rate until adulthood. During prenatal development,
F CSA increased about 5-fold from embryonic day (E)10.5 to E19.5, while the amount of MHC normalized to the amount of total protein
remained constant (from E13.5 to E19.5). This suggests that the development of structural organization of the myofilaments
during the embryonic and the fetal period may play an important role for the improvement of force generation. There was an
overall decrease of 0.5 pCa units in the Ca 2+ sensitivity of force generation from E13.5 to the adult, of which the main decrease (0.3 pCa units) occurred within a short
time interval, between E19.5 and 7 days after birth (7 days pn). Densitometric analysis of SDS-PAGE and Western blots revealed
that the major switches between troponin T (TnT) isoforms occur before E16.5, whereas the transition points of slow skeletal
troponin I (ssTnI) to cardiac TnI (cTnI) and of β-MHC to α-MHC both occur around birth, in temporal correlation with the main
decrease in Ca 2+ sensitivity. To test whether the changes in Ca 2+ sensitivity are solely based on Tn, the native Tn complex was replaced in fibres from E19.5 and adult hearts with fast skeletal
Tn complex (fsTn) purified from rabbit skeletal muscle. The difference in pre-replacement values of pCa 50 (âlog(Ca 2+ m â1 )) required for half-maximum force development) between E19.5 (6.05 ± 0.01) and adult fibres (5.64 ± 0.04) was fully abolished
after replacement with the exogenous skeletal Tn complex (pCa 50 = 6.12 ± 0.05 for both stages). This suggests that the major developmental changes in Ca 2+ sensitivity of skinned murine myocardium originate primarily from the switch of ssTnI to cTnI.
Developmental changes in force‐generating capacity and Ca2+ sensitivity of contraction in murine hearts were correlated with changes in myosin heavy chain (MHC) and troponin (Tn) isoform expression, ...using Triton‐skinned fibres. The maximum Ca2+‐activated isometric force normalized to the cross‐sectional area (FCSA) increased mainly during embryogenesis and continued to increase at a slower rate until adulthood. During prenatal development, FCSA increased about 5‐fold from embryonic day (E)10.5 to E19.5, while the amount of MHC normalized to the amount of total protein remained constant (from E13.5 to E19.5). This suggests that the development of structural organization of the myofilaments during the embryonic and the fetal period may play an important role for the improvement of force generation. There was an overall decrease of 0.5 pCa units in the Ca2+ sensitivity of force generation from E13.5 to the adult, of which the main decrease (0.3 pCa units) occurred within a short time interval, between E19.5 and 7 days after birth (7 days pn). Densitometric analysis of SDS‐PAGE and Western blots revealed that the major switches between troponin T (TnT) isoforms occur before E16.5, whereas the transition points of slow skeletal troponin I (ssTnI) to cardiac TnI (cTnI) and of β‐MHC to α‐MHC both occur around birth, in temporal correlation with the main decrease in Ca2+ sensitivity. To test whether the changes in Ca2+ sensitivity are solely based on Tn, the native Tn complex was replaced in fibres from E19.5 and adult hearts with fast skeletal Tn complex (fsTn) purified from rabbit skeletal muscle. The difference in pre‐replacement values of pCa50 (−log(Ca2+m−1)) required for half‐maximum force development) between E19.5 (6.05 ± 0.01) and adult fibres (5.64 ± 0.04) was fully abolished after replacement with the exogenous skeletal Tn complex (pCa50= 6.12 ± 0.05 for both stages). This suggests that the major developmental changes in Ca2+ sensitivity of skinned murine myocardium originate primarily from the switch of ssTnI to cTnI.
Cellular cardiomyoplasty is discussed as an alternative therapeutic approach to heart failure. To date, however, the functional characteristics of the transplanted cells, their contribution to heart ...function, and most importantly, the potential therapeutic benefit of this treatment remain unclear.
Murine ventricular cardiomyocytes (E12.5-E15.5) labeled with enhanced green fluorescent protein (EGFP) were transplanted into the cryoinjured left ventricular walls of 2-month-old male mice. Ultrastructural analysis of the cryoinfarction showed a complete loss of cardiomyocytes within 2 days and fibrotic healing within 7 days after injury. Two weeks after operation, EGFP-positive cardiomyocytes were engrafted throughout the wall of the lesioned myocardium. Morphological studies showed differentiation and formation of intercellular contacts. Furthermore, electrophysiological experiments on isolated EGFP-positive cardiomyocytes showed time-dependent differentiation with postnatal ventricular action potentials and intact beta-adrenergic modulation. These findings were corroborated by Western blotting, in which accelerated differentiation of the transplanted cells was detected on the basis of a switch in troponin I isoforms. When contractility was tested in muscle strips and heart function was assessed by use of echocardiography, a significant improvement of force generation and heart function was seen. These findings were supported by a clear improvement of survival of mice in the cardiomyoplasty group when a large group of animals was analyzed (n=153).
Transplanted embryonic cardiomyocytes engraft and display accelerated differentiation and intact cellular excitability. The present study demonstrates, as a proof of principle, that cellular cardiomyoplasty improves heart function and increases survival on myocardial injury.
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