Increased late sodium currents are related to transcription of neuronal isoforms in a pressure-overload model

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AimsThe late and persistent sodium current (INa) has been identified as a target for anti-arrhythmia drugs in patients with heart failure (HF). However, the underlying mechanism of late INa (INaL) production remains uncertain. We hypothesized that transcriptional alteration among sodium channel (NaCh) isoforms may contribute to INaL in failing cardiomyocytes.Methods and resultsPressure-overload rat models were created by 16-week constriction of the ascending aorta (HF). Haemodynamic and electrocardiographic variables were studied in sham operation and HF rats. Action potential (AP) and INa were recorded using whole-cell patch-clamp techniques. The expression of various NaCh isoforms was evaluated by immunocytochemistry, RT-PCR, and western blot. The HF group exhibited left ventricular enlargement, systolic dysfunction, and prolongation of QTc intervals (P < 0.05). Current-clamp recording indicated that AP durations (APDs) were more sensitive to tetrodotoxin. Voltage-clamp recordings showed that INaL was increased (−1.54 ± 0.43 vs. −1.08 ± 0.38 pA/pF, P < 0.01) in HF, but transient INa (INaT) density was decreased (−14.61 ± 2.30 vs. −26.15 ± 5.17 pA/pF, P < 0.01). Correspondingly, the relative mRNA levels of the neuronal isoforms SCN1a and SCN8a increased 2.5- and 2.7-fold, respectively; SCN3a did not change, whereas SCN5a decreased by ∼60% in HF. Protein levels paralleled their mRNA expression.ConclusionThe up-regulated expression of the neuronal NaCh isoforms SCN1a and SCN8a could be one mechanism of INaL production, which may contribute to prolongation of APD in the failing heart.

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