Molecular Mechanism for Excitation-contraction Coupling in Heart and its Pathophysiological Significance

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This study has been performed to elucidate a molecular mechanism for excitation-contraction coupling and examine the pathophysiological significance in heart diseases..1) We generated the tranagenic mice expressing a mutant SERCA2a lacking the interaction site with phospholamban. The both mice showed increased contraction as well as relaxation. Upon induction of pressure overload by transverse aortic constriction, the mutant mice developed less cardiac hypertrophy than littermate controls. The activation of Ca^<2+>-sensitive protein kinase C by pressure overload was significantly attenuated in the hearts.2) We have crossed foxed ryanodine receptor mice with MLC-2v Cre mice. The mice, which lack one allele of the gene, appeared normal. Western blot analysis revealed about 50% decrease in ryr2 protein level but no differences in SEACA, NCX, and CAQ. Echocardiography indicated that heterozygous ryr2 knockout mice showed no significant differences in chamber size and ejection fraction compared with wild type mice. Hemodynamic study also indicated ablation of one allele of the gene led to no alteration in cardiac function.3) We attempted to obtain cardiac-specific sorcin knockout mice, which has been known to interact both with dihidropyridine receptor and with ryanodine receptor. We, first, isolated mouse sorcine gene and analyzed it to obtain targeting construct. We inserted a flox sequence in the first and second exon and electroporated it into ES cells. As a result, we successly obtained floxed mice. We are on the way to analyze the mice after mating cardiac specific Cre mice.