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

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 IC(50) 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.