Abstract 31: Mutation of Tnni3k Gene Increased Incidence of Arrhythmias in Culture Cardiomyocytes and In Vivo Mouse Hearts

Aims : Our recent studies showed that overexpression of TNNI3K promoted cardiac myogenesis, enhanced cardiac performance, and protected the myocardium from ischemic injury. Here, we report that replaced serine of the 835 and 836th in the C-terminal modulation area of TNNI3K gene with alanine increased the incidence of arrhythmia outbreak in culture cardiomyocytes and in mouse hearts in vivo. Methods and results : Wild TNI3K and mutated TNNI3K gene obtained from substitution of serine at 835-836 sites with alanine (S835A, S836A) were transfected respectively into P19CL6 cells for differentiation into cardiomyocytes, or directly transfected into beating hearts for in vivo experiments. Then, beating rhythm and frequency were observed in the cardiomyocytes at 16 day after inducer or in the whole heart of mice. Results obtained from culture cardiomyocytes show that the incidence of arrhythmia-like beating activities including bigeminy, trigeminy and tachycardia was more frequent in the TNNI3K-mutant group than that in the wild-TNNI3K group (P<0.05). By the in vivo experiment, incidence of arrhythmic outbreak was examined in 1) control group (n=9) of the male C57BL6 mouse, 2) the wild TNNI3K group (n=12), 3) the mutant-TNNI3K gene group (n=12). Incidences of bigeminy (66.7%), tachycardia (50.0%) and bradycardia (41.9%) in the TNNI3K mutant group were significantly higher than that in the other two groups. To investigate possible mechanisms involved on the TNNI3K mutant-induced arrhythmias, intracellular Ca 2+ -response was investigated after application of ryanodine at concentrations of 1, 10, 20, and 50μM. The ryanodine-induced increase of Ca 2+ -concentrations in the wild group was stronger than that in the mutant group (P<0.05). Furthermore, action potentials of cultured cardiomyocytes were recorded with glass microelectrode techniques and data showed that the incidence of early or delayed afterdepolarization is significantly increased the mutant group (p<0.01). Conclusions : TNNI3K-mutation increased the incidences arrhythmias in cultured cardiomyocytes and in mouse hearts in vivo. Elucidation of the molecular mechanism involved would be useful for innovation of new anti-arrhythmic drugs.