| 研究実績の概要 |
In this fiscal year, our focus was on investigating the arrhythmogenicity induced by gain-of-function mutations and pathological activation of TRPM4 in Purkinje fibers (PF). We conducted voltage-jump experiments in HEK293 cells expressing the E7K and Q854R TRPM4 mutants under ionomycin-perforated cell-attached recording to mathematically model the altered gating of the mutants. The results showed that the mutants had increased voltage- and Ca2+-sensitivities, leading to a stabilized open state. Using a modified Trovato PF model in 1D cable simulations, we demonstrated that enhancing the density/activity of mutant channels progressively reduced AP conduction velocity, eventually leading to complete conduction block. Furthermore, 2D simulations with HL-1 atrial cardiomyocyte and cardiac fibroblast models revealed that the gain-of-function mutants could generate complex patterns of anisotropic AP propagation characterized by various degrees of local conduction blocks, fission, meander and fusion of excitation fronts, and ectopic excitations, particularly in the presence of tissue heterogeneity. These complex patterns represent a significant trend towards arrhythmias. Ex vivo experiments were performed in Langendorff perfused hearts, and the results showed that the TRPM4 selective blocker, 9-phenanthrol, strongly suppressed ventricular tachycardias induced by mechanical stimulation of endocardial PFs exposed to ischemia-reperfusion injury. These findings suggest a potential involvement of overactive TRPM4 channels in PFs and their contribution to arrhythmogenicity.
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