We have previously reported the existence of at least four troponin T isoforms in rabbit ventricular muscle and described the changes in their distribution with development. In this report we test whether the proportions of the troponin T isoforms are related to the sensitivity of the myofilaments to calcium. We measured the force-pCa relations in 12 detergent-skinned ventricular strands of cardiac muscle from newborn (2-5-day-old) rabbits. We determined from each strand the amount of each troponin T isoform relative to the total amount of troponin T by using sodium dodecyl sulfate-polyacrylamide gel electrophoresis and densitometric scans of Western blots probed with a cardiac-specific troponin T monoclonal antibody, MAb 13-11. To assess the presence of different relative amounts of cardiac and slow skeletal troponin I among the strands, we determined the amount of cardiac troponin I relative to tropomyosin. We determined the Hill coefficient and the pCa for half-maximal force, pCa50, for each strand. pCa50 was related directly to the relative amount of troponin T2 (pslope = 0.037). Our results do not indicate a relation between the Hill coefficient and troponin T2. We also did not find a relation between pCa50 and the cardiac troponin I/tropomyosin ratio, which suggests that the correlation between pCa50 and troponin T2 was not a result of changes in the relative amounts of cardiac and slow skeletal muscle troponin I. Our findings indicate that a relation exists between the force-pCa characteristics of rabbit myocardium and the troponin T isoforms that it expresses, suggesting a role for troponin T in modulating the sensitivity of cardiac myofilaments to calcium.

A number of studies indicate that females have a better reparative response in earlier stages of myocardial infarction (MI) compared to males. Nevertheless, little is known concerning the sex‐related differences in a later stage of MI healing (i.e. scar formation). Accordingly, we designed our study to determine whether the composition of the scar is affected by the biological sex of post‐MI animals. A large MI was induced in 12‐month‐old male (M‐MI) and female (F‐MI) Sprague‐Dawley rats by ligation of the left coronary artery. Four weeks after the MI, rats with transmural infarctions, greater than 50% of the left ventricular free wall, were evaluated. The fractional volume of fibrillar collagen (FC), cardiac myocytes (CM), myofibroblasts (MF) and vascular smooth muscle cells (VSMC) was determined in each scar. The mean scar size and thickness were comparable between F‐MI and M‐MI rats (61.3±3.9% vs. 63.8±2.5% and 0.66±0.04mm vs. 0.73±0.05mm, respectively). Although, there was a great degree of heterogeneity in spatial distribution of the analyzed structural components within each scar, their mean content showed no significant differences between F‐MI and M‐MI rats (FC: 53.3±6.6% vs. 61.6±4.5%; CM: 3.1±0.4% vs. 3.3±0.4%; MF: 9.6±1.2% vs. 9.6±1.7%; VSMC: 3.4±0.5 vs. 2.3±0.5%). Our data are the first to demonstrate that biological sex does not influence the structural composition of the MI scar in middle‐aged rats.Grant Funding Source: Internal Award from the NYCOM Office of Research (E.I. Dedkov) and NIH RO1‐HL62587 (R.J. Tomanek)