The functional consequences of sodium channel NaV 1.8 in human left ventricular hypertrophy

In hypertrophy and heart failure, the proarrhythmic persistent Na+ current (INaL ) is enhanced. We aimed to investigate the electrophysiological role of neuronal sodium channel NaV 1.8 in human hypertrophied myocardium.

We show for the first time that the neuronal sodium channel NaV 1.8 is up-regulated on mRNA and protein level in the human hypertrophied myocardium. Furthermore, inhibition of NaV 1.8 reduced augmented INaL , abbreviated the action potential duration, and decreased the SR-Ca2+ leak. The findings of our study suggest that NaV 1.8 could be a promising antiarrhythmic therapeutic target and merits further investigation.

Myocardial tissue of 24 patients suffering from symptomatic severe aortic stenosis and concomitant significant afterload-induced hypertrophy with preserved ejection fraction was used and compared with 12 healthy controls. We performed quantitative real-time PCR and western blot and detected a significant up-regulation of NaV 1.8 mRNA (2.34-fold) and protein expression (1.96-fold) in human hypertrophied myocardium compared with healthy hearts. Interestingly, NaV 1.5 protein expression was significantly reduced in parallel (0.60-fold). Using whole-cell patch-clamp technique, we found that the prominent INaL was significantly reduced after addition of novel NaV 1.8-specific blockers either A-803467 (30 nM) or PF-01247324 (1 μM) in human hypertrophic cardiomyocytes. This clearly demonstrates the relevant contribution of NaV 1.8 to this proarrhythmic current. We observed a significant action potential duration shortening and performed confocal microscopy, demonstrating a 50% decrease in proarrhythmic diastolic sarcoplasmic reticulum (SR)-Ca2+ leak and SR-Ca2+ spark frequency after exposure to both NaV 1.8 inhibitors. Conclusions: We show for the first time that the neuronal sodium channel NaV 1.8 is up-regulated on mRNA and protein level in the human hypertrophied myocardium. Furthermore, inhibition of NaV 1.8 reduced augmented INaL , abbreviated the action potential duration, and decreased the SR-Ca2+ leak. The findings of our study suggest that NaV 1.8 could be a promising antiarrhythmic therapeutic target and merits further investigation.