To study if GCH1 overexpression may reduce diabetes-induced impairments in intracellular Ca2+ signaling, we first measured intracellular [Ca2+]i in fura-2-loaded cardiomyocytes isolated from Tg and WT mice with or without diabetes 12 weeks after administration of STZ or vehicle (Fig. 5A). The gene discussed is GCH1; the disease is diabetes mellitus.