Background: The ras-related small G-protein Rad was originally identified from skeletal muscle of patients with type 2 diabetes mellitus. We have recently reported that Rad plays a critical role in generating arrhythmias. The study was aimed to elucidate the role of Rad in intracellular calcium homeostasis. Methods and Reslts: We developed the transgenic mice that overexpress S105N mutant Rad driven by α-myosin heavy chain promoter. We mesure intracellular Ca concentration ([Ca2+]I) from isolated cardiomyocytes by confocal microscopy. The amplitude of [Ca2+]I transient was significantly increased in S105N-Rad-TG cardiomyocytes, compared with littermate. Furthermore, the Ca2+ sparks and the spontaneous Ca2+ waves occurred with greater frequency in S105N-Rad-TG cells, implicating the enhanced activity of SERCA. We recorded L-type calcium currents (ICa-L) and action potentials (APs) from isolated cardiomyocytes using whole cell patch-clamp technique. The peak ICa-L was dramatically larger in the S105N-Rad-TG cells than in littermate. Early afterdepolarization (EAD) and delayed afterdepolarization (DAD) were frequently observed in S105N-Rad-TG. Then, the phosphorylation of RYR2 at Ser2809 and PKA was significantly enhanced in S105N-Rad-TG by Western blot. Conclusions: Our results provided the first evidence that Rad might regulate RYR2 activity possibly via downstream of PKA signaling pathway.
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