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

Abstract

Studies have shown that fish oils, containing n-3 fatty acids, have protective effects against ischemiainduced, 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,␣ ) in human embryonic kidney (HEK293t) cells transfected with the ␣-subunit of the human cardiac Na ؉ channel (hH1 ␣ ). Extracellular application of 0.01 to 30 M eicosapentaenoic acid (EPA, C20:5n-3) significantly reduced I Na,␣ with an IC 50 of 0.51 ؎ 0.06 M. The EPAinduced suppression of I Na,␣ was concentration-and voltagedependent. EPA at 5 M 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,␣ with a higher ''binding affinity'' to hH1 ␣ 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 M EPA. The time for 50% recovery from the inactivation state was significantly slower in the presence of 5 M 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,␣ were reversible. Furthermore, docosahexaenoic acid (C22:6n-3), ␣-linolenic acid (C18:3n-3), conjugated linoleic acid (C18:2n-7), and oleic acid (C18:1n-9) at 5 M and all-trans-retinoic acid at 10 M had similar effects on I Na,␣ as EPA. Even 5 M of stearic acid (C18:0) or palmitic acid (C16:0) also significantly inhibited I Na,␣ . In contrast, 5 M EPA ethyl ester did not alter I Na,␣ (8 ؎ 4%, n ‫؍‬ 8, P > 0.05). The present data demonstrate that free fatty acids suppress I Na,␣ with high ''binding affinity'' to hH1 ␣ channels in the inactivated state and prolong the duration of recovery from inactivation.Dietary long chain polyunsaturated fatty acids (PUFAs) are able to prevent ischemia-induced fatal arrhythmias in animals (1-4) and probably in humans (5-7). Their antiarrhythmic actions have been demonstrated in cultured cardiac myocyte preparations in the absence of neuronal or humoral influences (8) and have been shown to result from a stabilizing effect of the PUFAs on the electrophysiology of each individual myocyte (9). The electrophysiologic effects of the PUFAs in turn are caused by their modulation of several ion currents through the plasma membrane of the cardiomyocytes (10-12). One of the ion currents affected by the PUFAs is the voltagedependent, fast sodium current, I Na (10), which is responsible for initiating the action potential in cells of excitable tissues. Thus the effects of the PUFAs on I Na must constitute an important factor in the ability of the PUFAs to prevent or terminate fatal cardiac arrhythmias.We have used whole-cell voltage-clamp studies on cultured neonatal rat cardiomyocytes to examine the effects of the PUFAs on I Na and have found that in their free fatty acid form they rapidly and strongly suppress I Na and prolong the duration of the inac...

Subchronic Alpha-Linolenic Acid Treatment Enhances Brain Plasticity and Exerts an Antidepressant Effect: A Versatile Potential Therapy for Stroke

“…In the domain of stroke disorders, there is growing evidence that the omega-3 precursor, ALA, is a potent protector in several models of global and focal ischemia (Xiao et al, 1998;Lauritzen et al, 2000;Blondeau et al, 2001Blondeau et al, , 2002Blondeau et al, , 2007Lang-Lazdunski et al, 2003;Heurteaux et al, 2004Heurteaux et al, , 2006a. In a mouse model of stroke, we found that a single injection of ALA, after the onset of stroke, significantly reduced infarct size and improved the neurological score 24-h post-ischemia.…”

Single point mutations affect fatty acid block of human myocardial sodium channel α subunit Na + channels

“…Concentrations of ethanol used for dissolving fatty acids were negligible and had no effect on Na ϩ currents in HEK293t cells. Currents were acquired and analyzed as before (3,5). Experiments were conducted at 22-23°C.…”

“…Recent data demonstrated that PUFAs significantly shifted the steady-state inactivation of cardiac Na ϩ currents to more hyperpolarized values (3,5,6). To test whether single point mutations altered the EPA-induced shift of the steady-state inactivation, we investigated the effects of different concentrations of EPA on inactivation of the wild type and its three mutants of hH1 ␣ Na ϩ channels.…”

“…We had demonstrated that PUFAs produced a voltage-dependent inhibition of cardiac Na ϩ currents in cardiomyocytes and in HEK293t cells expressing hH1 ␣ or hH1 ␣ plus ␤ 1 (3,5,6). To learn whether the effects of the PUFAs on these mutated channels would follow the same pattern of inhibition, we assessed whether single point mutations modified the EPA-induced voltage-dependent inhibition.…”

Nutrients: the environmental regulation of cardiovascular gene expression

“…In contrast, the knowledge concerning the anti-inflammatory effects of x-3 PUFAs on the myocardium is limited to a potent anti-arrhythmic action that has been described both in vivo on myocardium [38,40] and in vitro on cardiomyocytes [26,31]. The presence of PUFAs in cardiomyocyte membrane phospholipids modulates Na + , K + and Ca 2+ channels' activity [62,63] causing an electric stabilization of cells and thus prevention of arrhythmias.…”