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Trimeric intracellular cation channels, called TRIC-A and TRIC-B, are distributed to intracellular Ca2+ stores and mainly mediate the permeability of K+ ions in multiple cell types. Previously we showed that genetic ablation of TRIC-A leads to compromised K+-permeability and Ca2+ release in the muscle sarcoplasmic reticulum (SR), supporting the hypothesis that TRIC channels function as counter-ion channels during the acute phase of Ca2+ release under physiological conditions. In cardiomyocytes, spontaneous Ca2+ waves, triggered by store overload-induced Ca2+ release (SOICR) mediated by the type 2 ryanodine receptor (RyR2), develop extra-systolic contractions often associated with arrhythmic events. In this study, we found that the carboxyl-terminal tail domain of TRIC-A (CTT-A) interacts with the RyR2 channel to directly modulate SOICR activity. Biochemical studies demonstrate direct interaction between CTT-A and RyR2. In HEK293 cells with stable expression of RyR2, transient expression of TRIC-A, but not TRIC-B, leads to apparent suppression of spontaneous Ca2+ oscillations. Ca2+ measurements using the cytosolic indicator Fura-2 and the ER luminal store indicator D1ER suggest that TRIC-A enhances Ca2+ leak across the ER membrane by directly targeting to RyR2 to modulate SOICR. Moreover, synthetic CTT-A peptide facilitates RyR2 channel activity in the lipid bilayer reconstitution system and induces intracellular Ca2+ release after micro-injection into isolated cardiomyocytes, whereas such effects were not observed with the CTT-B peptide. Therefore, in addition to the ion-conducting function, TRIC-A seems to function as an accessory protein of RyR2 to modulate SR Ca2+ handling in cardiac muscle. Although Tric-a-/- mice do not display significant abnormity in the heart under resting condition, isoproterenol induced stress condition would induce abnormal cardiac function and fibrosis. Moreover, Tric-a-/- heart is more susceptible to Transverse Aortic Constriction (TAC) induced heart injury and develop cardiac fibrosis and hypertrophy. These results suggested that the stress resistance capacity is significantly compromised in Tric-a-/- heart. Using isolated cardiomyocytes, we indentified altered SR Ca2+ uptake as well as altered mitochondria Ca2+ uptake in the Tric-a-/- cardiomyocytes indicating that TRIC-A played a role in SR-mitochondria Ca2+ cross-talk. In summary, our results demonstrate the crucial role of TRIC-A in regulating both SR and mitochondria Ca2+ homeostasis. TRIC-A could directly interact with RyR2 and regulate its activity to maintain normal SR Ca2+ homeostasis. Cardiomyocytes lacking TRIC-A would not only cause impaired SR Ca2+ signaling, but also affect mitochondria Ca2+ homeostasis through SR-mitochondria cross-talk which leads to compromised mitochondria stability under stress condition and ultimately results in cardiac fibrosis and hypertrophy.

Investment bi-metal casting is a newly developed casting process and is prone to have more defects. Process optimization based on a computer simulation model is critical to obtain high quality castings. To obtain an accurate defect prediction analytically in the bi-metal casting part relies on the full consideration of the entire physical phenomenon during the process. It is also important to reduce the simulation time cost of the optimization process in order to make it practically achievable. This dissertation first presents the methods to develop a representative computer simulation model of the investment bi-metal casting process to predict the existing defects, such as: cracks, porosity, cold shut, hot tearing, deformation, etc. The model has been validated by experimental data. Secondly, this dissertation presents an integrated low time cost approach to optimize the investment bi-metal casting process based on the computer simulation model. As a case study, by employing the integrated optimization technology, an investment bi-metal casting process of a Spiral Flight is optimized to obtain better process specifications. The Monte Carlo analysis of the original and optimal process shows a significant improvement of the casting result.