Impact of E163R cTnT mutation on cardiac mechanics and energetics in a murine model

Introduction: Many of cTnT mutations linked to cardiomyopathies fall the TNT1 domain/N terminal tail region of unresolved high definition structure. This region (~94-170) of cTnT is critical to Tm binding and contraction regulation. Here, the impact of the E163R mutation in cTnT-TNT1 on contractile function and tension cost was investigated using intact and skinned preparations from WT and transgenic mouse hearts. Methods: Left and right ventricular trabeculae were dissected from nontransgenic wild type (WT) and heterozygous (D160E or E163R) mouse hearts and mounted isometrically to record twitch tension or, when skinned, Ca2þ activated force. Myofibrillar ATPase activity was measured by fluorimetric enzyme coupled assay (de Tombe and Stienen, 1995). Results: Myocardium of E163R mice shows: (i) no change of myosin isoform expression (ii) maintained peak isomentric twitch tension at all stimulation frequencies, (iii) prolonged time to peak and time to 50% relaxation, with preserved rate-adaptation of twitch duration, (iv) changes of the short-term interval force relationship and increased occurrence of spontaneous contractions. No significant differences were found in maximum Ca2þ activated tension of E163R and WT skinned trabeculae. However, Ca2þ sensitivity of tension was significantly increased in E163R skinned trabeculae when compared with WT. As to the economy of force maintenance, preliminary experiments suggest an increase of tension cost in trabeculae from E163R hearts. Resting ATPase activity also tended to be higher in E163R preparations. Kinetics of force development and relaxation will be assessed on single myofibrils, isolated from the same hearts. Conclusions: Both primary sarcomeric changes and secondary E-C coupling alterations contribute to mechanical impairment in E163R cTnT mutant myocardium. Supported by: EC Grant n. 241577 (BIG-Heart)