Force-pCa Relation and Troponin T Isoforms of Rabbit Myocardium

• Published in: Circulation research 1991-12, Vol.69 (6), p.1470-1475
• Main Authors: Nassar, Rashid, Malouf, Nadia N, Kelly, Michael B, Oakeley, Annette E, Anderson, Page A.W
• Format: Article
• Language: English
• Subjects: Animals; Animals, Newborn; Biological and medical sciences; Blotting, Western; Calcium - physiology; Fundamental and applied biological sciences. Psychology; Heart; Heart - physiology; In Vitro Techniques; Myocardial Contraction; Rabbits; Troponin - chemistry; Troponin - physiology; Troponin T; Vertebrates: cardiovascular system
• ISSN: 0009-7330; 1524-4571
• DOI: 10.1161/01.RES.69.6.1470

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 she 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.