Fatty Acid Ethyl Esters, Nonoxidative Metabolites of Ethanol, Accelerate the Kinetics of Activation of the Human Brain Delayed Rectifier K+ Channel, Kv1.1

Abstract

Herein we demonstrate that the major metabolites of ethanol in neural tissues, fatty acid ethyl esters, dramatically accelerate the kinetics of the voltage-induced activation of the human brain delayed rectifier potassium channel, Kv1.1. Specifically, the external application of ethyl oleate (20 M) to Sf9 cells expressing the recombinant Kv1.1 channel resulted in a decrease in the rise times of the macroscopic current (e.g. from 51.7 ؎ 13.1 to 12.8 ؎ 3.0 ms at 0 mV for 10 -90% rise times) and a 10-mV hyperpolarizing shift (at 0 mV) in the voltage dependence of channel activation. These effects were dose-dependent (half-maximal effect at 7 M), saturable and specific (i.e. fatty acid methyl esters were without effect). Although application of either ethanol or oleic acid alone did not result in alterations of the activation kinetics, the concomitant application of ethanol and oleic acid reproduced the effects of fatty acid ethyl esters with a temporal course which paralleled the intracellular accumulation of fatty acid ethyl esters in Sf9 cells. Moreover, application of fatty acid ethyl esters (but not ethanol) to rat hippocampal cells in culture produced similar effects on hippocampal delayed rectifier currents. Collectively, these results demonstrate that pathophysiologically relevant concentrations of metabolites of ethanol, fatty acid ethyl esters, modulate the function of a prototypic neuronal ion channel and thus likely contribute to the pathophysiologic sequelae of ethanol abuse in excitable tissues.Elucidation of the biochemical mechanisms underlying the effects of ethanol in electrically excitable tissues has been a long standing goal in neurochemistry (e.g. Refs. 1-3). Due to the structural simplicity of ethanol, the difficulties in identifying the precise biochemical mechanisms responsible for ethanol-induced alterations in electrophysiologic function have represented a fundamental paradox in neuropharmacology. Although multiple effects of ethanol on ion channel function have been demonstrated, consistent alterations in ion channel properties at pathophysiologically relevant concentrations of ethanol (i.e. 0.01-0.1% (2-20 mM)) have not been forthcoming (4 -7). The discordance between the amounts of ethanol necessary to modulate ion channel function in isolated cells and that necessary for perturbation of electrophysiologic function in intact neural structures represents an unresolved and highly controversial issue in the pathobiology of alcohol.Fatty acid ethyl esters are the major nonoxidative metabolite of ethanol in humans and represent the predominant ethanol metabolite in human brain after alcohol ingestion (8 -10). Moreover, detailed examination of fatty acid ethyl ester synthesis in distinct anatomic loci in brain has demonstrated a high correlation between ethanol-induced pathology and the metabolic rates of fatty acid ethyl ester production (11). Since recent studies have identified the electrophysiologic effects of nonesterified fatty acids on ion channels (12-17), we hypothesized that some of...

Stimulatory and inhibitory effects of ethanol on hippocampal acetylcholine release

“…Nicotinic receptors are also modulated by ethanol (Fröhlich et al 1994;Nagata et al 1996). Finally, pharmacological effects of non-oxidative metabolites of ethanol in the brain, such as fatty acid ethyl esters (Gubitosi-Klug and Gross 1996) and phosphatidylethanol (Gustavsson, 1995) must be considered. Further studies are required to elucidate the molecular mechanisms of ethanol's effects on the septohippocampal pathway.…”

Dependence of 6β-acetoxy-7α-hydroxyroyleanone block of Kv1.2 channels on C-type inactivation

“…However, linoleic acid also affects activation gating by causing a leftshift in the activation curve. Arachidonic acid, a lipid signaling molecule arising from phospholipid metabolism, induces fast inactivation of otherwise non-inactivating Kv channels (Kv1.1 and 3.1) [15] but it also accelerates activation of Kv1.1 [16]. There are other compounds, namely ginsenoside Rg 3 and verapamil, which appear to block Kv channels by accelerating C-type inactivation [22,23].…”

“…channels. Other compounds which have been reported to modify (accelerate) C-type inactivation but also somewhat affect activation gating behaviors include KN-93, linoleic acid, and arachidonic acid [13][14][15][16]. We previously reported that HMJ-53A blocks Kv channels extracellularly by accelerating the closing of the inactivation gate [17].…”

The human Kv1.1 channel is palmitoylated, modulating voltage sensing: Identification of a palmitoylation consensus sequence

“…Whole-cell voltage clamp recordings of Sf9 cells were performed by using standard techniques as described (28)(29)(30)(31). Sf9 cells lack any depolarization-induced current and, therefore, provide a null background for determination of voltage-activated potassium channels (26,28).…”