Modulation of muscle rNa_v1.4 Na⁺ channel isoform by arachidonic acid and its non‐metabolized analog

Abstract

Arachidonic acid (AA) and its metabolic products are important second messengers which exert many biological actions, including modulation of various ion channels. However, the blockage of muscle Na(+) channel isoforms by AA has not been examined in detail. Here, we investigated the modulating effects of AA on muscle rNa(V)1.4 isoforms expressed in human embryonic kidney 293 cells. The results revealed that AA has both activation and inhibitory effects on rNa(V)1.4 currents depending on the depolarizing potential: AA increased the rNa(V)1.4 current evoked by a depolarization of -30 or -40 mV, but significantly decreased the rNa(V)1.4 current evoked by a depolarization of membrane potential over -10 mV. At concentrations of 1-500 microM, the inhibitory effect on the rNa(V)1.4 current induced by AA was dose-dependent and reversible. In addition to modulating the amplitude of the rNa(V)1.4 current, AA significantly modulated the steady-state activation and inactivation properties of rNa(V)1.4 channels. Furthermore, treatment with AA resulted in a fairly slow recovery of the rNa(V)1.4 channel from inactivation; however, the inhibitory effect of AA was not changed by repetitive pulses or by changing frequency. The effect of AA on rNa(V)1.4 currents was completely mimicked by ETYA, the non-metabolized analog of AA. Our data demonstrated that AA, but not the metabolic products of AA, can voltage-dependent modulate rNa(V)1.4 currents.

Fatty Acid Regulation of Voltage- and Ligand-Gated Ion Channel Function

“…The activation effect was observed over 120 min, suggesting that neo-synthesis and trafficking/insertion of new channels to/in the cell membrane could occur during this period, alone or in combination with unmasking of reserve channels already present in the plasmalemma (Wieland et al, 1996). This dual mechanism was also observed in the muscle rNa(V)1.4 channel isoform, which appears to depend on the depolarizing potential: AA, but not its metabolites, increased the channel current evoked by a −30 or −40 mV depolarization of the membrane potential, but significantly decreased it by a depolarization over −10 mV (Gu et al, 2009). It was also reported that cis -unsaturated FFA with a double bond at position 9 have a biphasic effect on connexin 46 hemichannels: current activation at low FFA concentration and current inhibition at higher concentrations, the effect being directly proportional to the number of double bonds (Retamar et al, 2011).…”

Arachidonic acid supplementation enhances in vitro skeletal muscle cell growth via a COX-2-dependent pathway

“…Provision of exogenous free AA substrate has been reported to directly influence MAPK signaling (1), intracellular Ca 2ϩ concentrations (9,58), and Na ϩ /K ϩ currents (8,11,18) in other cell types, all of which may be relevant to the control of skeletal muscle cell growth. In these studies the effect of supplemental AA was mimicked by the nonmetabolizable AA analog ETYA, inferring a response to AA independent of the synthesis of bioactive lipid mediators (1,8,9,11,18,58). An important consideration in the present study was thus whether the effects were mediated by AA or one or more downstream metabolites.…”

“…Eicosatetraynoic acid (ETYA; Cayman Chemicals), a structural, yet nonmetabolizable, analog of AA, was used as previously described to assess the requirement of downstream AA metabolism in the cellular response to AA treatment (1,8,11,18). Cells were treated in parallel with equivalent doses of ETYA or AA in select experiments.…”

“…As a nonmetabolizable analog, ETYA acts as a nonspecific COX/LOX inhibitor by competing with AA for enzyme binding. However, certain physiological effects induced by AA have also been reported to be mimicked by ETYA (1,8,11,18). The effect of AA in such cases has been considered to be independent of its metabolism.…”

Actions and Mechanisms of Polyunsaturated Fatty Acids on Voltage-Gated Ion Channels

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