Background:
Acute ethanol exposure impairs cardiac function, but the underlying cellular mechanisms remain incompletely understood. Late sodium current (late INa) enhancement may trigger Na⁺ overload, sarcoplasmic reticulum (SR) Ca²⁺ depletion, and contractile dysfunction. We investigated the effects of ethanol on Na⁺/Ca²⁺ homeostasis and contractility in failing human and murine ventricular cardiomyocytes and tested whether ranolazine confers protection.
Methods:
Isolated human failing ventricular cardiomyocytes and murine ventricular myocytes were exposed acutely to ethanol (3 ‰) ± ranolazine (10µM). Late INa was measured via patch-clamp, cytosolic Na⁺ via SBFI ratios, and Ca²⁺ transients via Fura2-AM fluorescence imaging. Contractility was assessed as twitch amplitude. Human failing ventricular trabeculae were analyzed for developed tension. CaMKII and NaV1.5 phosphorylation were determined by Western blot in human failing ventricular tissue. Ca²⁺ sparks were recorded in murine myocytes, including S571A knock-in mice with a phosphoresistant mutation at serine 571 of NaV1.5.
Results:
Ethanol markedly increased late INa in human failing cardiomyocytes (-75.8±3.6 vs. -54.7±8.0 A/F*ms, p=0.01), resulting in cytosolic Na⁺ overload in murine myocytes (1.1±0.03 vs. 0.97±0.02, p=0.006), both prevented by ranolazine (late INa: -36.1±5.7 A/F*ms, p=0.001 vs. EtOH, Na⁺: 0.95±0.02, p=0.004 vs. EtOH). Ethanol reduced Ca²⁺ transient amplitude (0.39±0.05 vs. 0.68±0.07, p=0.03) and SR Ca²⁺ content (0.56±0.08 vs. 1.1±0.08, p=0.02), causing a 3.6-fold decrease in twitch amplitude (1.5 ± 0.2 vs. 5.4 ± 0.9%, p=0.003), which was restored by ranolazine (4.6 ± 0.8%, p=0.007 vs. EtOH). In human trabeculae, ethanol impaired developed tension (0.96±0.2 vs. 2.5±0.4 mN/mm², p=0.04), fully prevented by ranolazine (2.4±0.6 mN/mm², p=0.04 vs. EtOH). Mechanistically, ethanol increased CaMKII T287 (0.7±0.2 vs. 0.4±0.1, p=0.04) and NaV1.5 S571 phosphorylation (0.5±0.1 vs. 0.1±0.05, p=0.04) in human ventricular tissue. Ethanol elevated Ca²⁺ spark frequency in murine cardiomyocytes (1.1±0.08 vs. 0.8±0.08 1/100 µm-1 s-1, p=0.04), prevented by ranolazine (0.8±0.09 1/100 µm-1 s-1, p=0.04 vs. EtOH) and dantrolene (0.8±0.1 1/100 µm-1 s-1, p=0.04 vs. EtOH). Late INa enhancement was inhibited by ranolazine (-29.1±3.0 vs. -69.9±2.8 A/F*ms in EtOH, p<0.0001) but not dantrolene (-55.8±4.0 A/F*ms, p<0.0001 vs. EtOH+Ran), indicating late INa as a central mechanism and upstream of SR Ca²⁺ leak. In S571A mice, ethanol failed to increase late INa (-25.9±4.8 vs. -23.6±2.4 A/F*ms, p=n.s.) or Ca²⁺ spark frequency (1.0±0.2 vs. 1.1±0.1 1/100 µm-1 s-1, p=n.s.), confirming S571 phosphorylation is essential for ethanol-induced dysfunction.
Conclusion:
Acute ethanol exposure impairs cardiac contractility via NaV1.5 S571-dependent late INa enhancement, leading to Na⁺ overload, SR Ca²⁺ depletion, and reduced contractile function. Ranolazine prevents these alterations in both isolated myocytes and multicellular human trabeculae, highlighting its potential as a targeted cardioprotective therapy in alcohol-induced cardiac dysfunction.
