Fatty acids suppress voltage-gated Na+ currents in HEK293t cells transfected with the α-subunit of the human cardiac Na+ channel

Fatty acids suppress voltage-gated Na⁺ currents in HEK293t cells transfected with the α-subunit of the human cardiac Na⁺ channel

^†The Charles A. Dana Research Institute and Harvard-Thorndike Laboratory, Cardiovascular Division, Department of Medicine, Beth Israel Deaconess Medical Center, Boston, MA 02215; ^§Department of Anesthesia, Brigham and Women’s Hospital, Boston, MA 02115; ^‡Department of Medicine, Massachusetts General Hospital, Boston, MA 02114; and ^*Harvard Medical School, Boston, MA 02215

Contributed by Alexander Leaf

Abstract

Studies have shown that fish oils, containing n-3 fatty acids, have protective effects against ischemia-induced, fatal cardiac arrhythmias in animals and perhaps in humans. In this study we used the whole-cell voltage-clamp technique to assess the effects of dietary, free long-chain fatty acids on the Na⁺ current (I_Na,α) in human embryonic kidney (HEK293t) cells transfected with the α-subunit of the human cardiac Na⁺ channel (hH1_α). Extracellular application of 0.01 to 30 μM eicosapentaenoic acid (EPA, C20:5n-3) significantly reduced I_Na,α with an IC₅₀ of 0.51 ± 0.06 μM. The EPA-induced suppression of I_Na,α was concentration- and voltage-dependent. EPA at 5 μM significantly shifted the steady-state inactivation relationship by −27.8 ± 1.2 mV (n = 6, P < 0.0001) at the V_1/2 point. In addition, EPA blocked I_Na,α with a higher “binding affinity” to hH1_α channels in the inactivated state than in the resting state. The transition from the resting state to the inactivated state was markedly accelerated in the presence of 5 μM EPA. The time for 50% recovery from the inactivation state was significantly slower in the presence of 5 μM EPA, from 2.1 ± 0.8 ms for control to 34.8 ± 2.1 ms (n = 5, P < 0.001). The effects of EPA on I_Na,α were reversible. Furthermore, docosahexaenoic acid (C22:6n-3), α-linolenic acid (C18:3n-3), conjugated linoleic acid (C18:2n-7), and oleic acid (C18:1n-9) at 5 μM and all-trans-retinoic acid at 10 μM had similar effects on I_Na,α as EPA. Even 5 μM of stearic acid (C18:0) or palmitic acid (C16:0) also significantly inhibited I_Na,α. In contrast, 5 μM EPA ethyl ester did not alter I_Na,α (8 ± 4%, n = 8, P > 0.05). The present data demonstrate that free fatty acids suppress I_Na,α with high “binding affinity” to hH1_α channels in the inactivated state and prolong the duration of recovery from inactivation.

Footnotes

↵ ¶ To whom reprint requests should be addressed at: 4th floor, 146 13th Street, Charlestown, MA 02129. e-mail: leaf.alexander1{at}mgh.harvard.edu.
ABBREVIATIONS:

EPA,

eicosapentaenoic acid;

INa,α,

the Na+ current of HEK293t cells transfected with the α-subunit of the human cardiac Na+ channel, hH1α;

PUFAs,

long chain polyunsaturated fatty acids;

HEK,

human embryonic kidney