Catecholaminergic polymorphic ventricular tachycardia (CPVT) is an inherited arrhythmogenic disease so far related to mutations in the cardiac ryanodine receptor (RYR2) or the cardiac calsequestrin (CASQ2) genes. Because mutations in RYR2 or in CASQ2 are not retrieved in all CPVT cases, we searched for mutations in the physiological protein partners of RyR2 and CSQ2 in a large cohort of CPVT patients with no detected mutation in these two genes. Based on a candidate gene approach, we focused our investigations on triadin and junctin, two proteins that link RyR2 and CSQ2. Mutations in the triadin (TRDN) and in the junctin (ASPH) genes were searched in a cohort of 97 CPVT patients. We identified three mutations in triadin which cosegregated with the disease on a recessive mode of transmission in two families, but no mutation was found in junctin. Two TRDN mutations, a 4 bp deletion and a nonsense mutation, resulted in premature stop codons; the third mutation, a p.T59R missense mutation, was further studied. Expression of the p.T59R mutant in COS-7 cells resulted in intracellular retention and degradation of the mutant protein. This was confirmed after in vivo expression of the mutant triadin in triadin knock-out mice by viral transduction. In this work, we identified TRDN as a new gene responsible for an autosomal recessive form of CPVT. The mutations identified in the two families lead to the absence of the protein, thereby demonstrating the importance of triadin for the normal function of the cardiac calcium release complex in humans.

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Background-An emerging concept is that a neuronal isoform of nitric oxide synthase (NOS1) may regulate myocardial contractility. However, a role for NOS1-derived nitric oxide (NO) in heart failure (HF) has not been defined. Methods and Results-Using a model of myocardial infarction-induced HF, we demonstrated that cardiac NOS1 expression and activity increased in HF rats (PϽ0.05 and PϽ0.001 versus shams, respectively). This was associated with translocation of NOS1 from the ryanodine receptor to the sarcolemma through interactions with caveolin-3 in HF hearts. With ex vivo and in vivo pressure-volume analysis, cardiac NOS1-derived NO was found to be negatively inotropic in shams but not HF hearts. Ventricular elastance (E es ) was significantly reduced in HF rats (PϽ0.05), and , the time constant of left ventricular relaxation, was prolonged (both PϽ0.05). Acute NOS1 inhibition significantly increased E es by 33Ϯ3% and by 17Ϯ2% (PϽ0.05) in shams, although these effects were significantly attenuated in HF hearts. ␤-Adrenergic stimulation induced a marked increase in systolic performance in sham hearts, with the responses being significantly blunted in HF hearts. E es increased by 163Ϯ42% (PϽ0.01) in sham hearts and 56Ϯ9% in HF hearts, and LV ϩdP/dt increased by 97Ϯ9% (PϽ0.01) in shams and 37Ϯ7% (PϽ0.05) in the HF group. Interestingly, preferential NOS1 inhibition enhanced the blunted responses of LV ϩdP/dt and E es to ␤-adrenergic stimulation in HF rats but had no effect in shams. Conclusions-These results provide the first evidence that increased NOS1-derived NO production may play a role in the autocrine regulation of myocardial contractility in HF.