Ranolazine normalizes action potential duration in angiotensin II exposed HL-1 cells: role of late sodium current

Purpose: Late sodium current (INaL) has been shown to play a key role in action potential (AP) prolongation and arrhythmogenesis in acquired and congenital cardiac diseases. However, the molecular signals leading to enhanced INaL are unknown. Locally increased angiotensin II (ANG II) participates to the pathogenesis of heart rhythm dysfunction, including atrial fibrillation. The aim of this study was to investigate whether exposure of immortalized atrial cells (HL-1) to ANG II could increase INaL therefore causing AP prolongation. At the same time, we assessed whether acute treatment with ranolazine, a selective blocker of INaL, was able to revert AP prolongation in ANG II exposed cells. Methods: HL-1 cells were incubated for 48 hours at 37C in the presence and absence (CTR) of 100 nM ANG II. INaL and AP duration (APD) were measured in patch-clamped cells at 37C. INaL was analysed in CTR and ANG II cells as a tedrodotoxin (TTX)-sensitive current obtained by subtraction of current recorded before and after application of 30 µM TTX. Finally, APD was measured in CTR and ANG II cells in the presence and absence of 10 µM ranolazine. Results: Enhanced INaL was observed in ANG II treated cells (Figure). Peak INaL at -50 mV was -2.1 pA/pF (n=5) in ANG II and -0.4 pA/pF (n=4) in CTR, respectively (p=0.04). Accordingly, APD measurements revealed a significant AP prolongation in ANG II compared to CTR (APD90: ANG II (n=14) 145.720.5 ms vs CTR (n=9) 92.8 4.6 ms). Acute application of 10 µM ranolazine significantly reduced APD in ANG II cells (APD90: 134.2±38.4 ms vs 190.6±39.5 ms, n=4), without affecting APD in CTR cells (APD90: 98.4±8.2 ms vs 100.7±21.4 ms, n=3). Conclusions: Increased levels of ANG II, as observed in several cardiac diseases, including atrial fibrillation, prolonged APD in HL-1 cells. This prolongation was INaL-dependent. Acute exposure to ranolazine was able to reduce AP prolongation following ANG II exposure.