Docosahexaenoic acid block of neuronal voltage-gated K+ channels: subunit selective antagonism by zinc

In Silico Screening Identification of Fatty Acids and Fatty Acid Derivatives with Antiseizure Activity: In Vitro and In Vivo Validation

High fat diets have been used as complementary treatments for seizure disorders for more than a century. Moreover, many fatty acids and derivatives, including the broad-spectrum antiseizure medication valproic acid, have been explored and used as pharmacological agents to treat epilepsy. In this work, we have explored the anticonvulsant potential of a large library of fatty acids and fatty acid derivatives, the LIPID MAPS Structure Database, using structure-based virtual screening to assess their ability to block the voltage-gated sodium channel 1.2 (NaV1.2), a validated target for antiseizure medications. Four of the resulting in silico hits were submitted for experimental confirmation using in vitro patch clamp experiments, and their protective role was evaluated in an acute mice seizure model, the Maximal Electroshock seizure model. These four compounds were found to protect mice against seizures. Two of them exhibited blocking effects on NaV1.2, CaV2.2, and CaV3.1.

Expression Pattern of ALOXE3 in Mouse Brain Suggests Its Relationship with Seizure Susceptibility

Arachidonic acid (AA), a polyunsaturated fatty acid, is involved in the modulation of neuronal excitability in the brain. Arachidonate lipoxygenase 3 (ALOXE3), a critical enzyme in the AA metabolic pathway, catalyzes the derivate of AA into hepoxilins. However, the expression pattern of ALOXE3 and its role in the brain has not been described until now. Here we showed that the levels of Aloxe3 mRNA and protein kept increasing since birth and reached the highest level at postnatal day 30 in the mouse hippocampus and temporal cortex. Histomorphological analyses indicated that ALOXE3 was enriched in adult hippocampus, somatosensory cortex and striatum. The distribution was restricted to the neurites of function-specific subregions, such as mossy fibre connecting hilus and CA3 neurons, termini of Schaffer collateral projections, and the layers III and IV of somatosensory cortex. The spatiotemporal expression pattern of ALOXE3 suggests its potential role in the modulation of neural excitability and seizure susceptibility. In fact, decreased expression of ALOXE3 and elevated concentration of AA in the hippocampus was found after status epilepticus (SE) induced by pilocarpine. Local overexpression of ALOXE3 via adeno-associated virus gene transfer restored the elevated AA level induced by SE, alleviated seizure severities by increasing the latencies to myclonic switch, clonic convulsions and tonic hindlimb extensions, and decreased the mortality rate in the pilocarpine-induced SE model. These results suggest that the expression of ALOXE3 is a crucial regulator of AA metabolism in brain, and potentially acts as a regulator of neural excitability, thereby controlling brain development and seizure susceptibility.

Roles of endogenous ether lipids and associated PUFAs in the regulation of ion channels and their relevance for disease

Ether lipids (ELs) are lipids characterized by the presence of either an ether linkage (alkyl lipids) or a vinyl ether linkage [i.e., plasmalogens (Pls)] at the sn1 position of the glycerol backbone, and they are enriched in PUFAs at the sn2 position. In this review, we highlight that ELs have various biological functions, act as a reservoir for second messengers (such as PUFAs) and have roles in many diseases. Some of the biological effects of ELs may be associated with their ability to regulate ion channels that control excitation-contraction/secretion/mobility coupling and therefore cell physiology. These channels are embedded in lipid membranes, and lipids can regulate their activities directly or indirectly as second messengers or by incorporating into membranes. Interestingly, ELs and EL-derived PUFAs have been reported to play a key role in several pathologies, including neurological disorders, cardiovascular diseases, and cancers. Investigations leading to a better understanding of their mechanisms of action in pathologies have opened a new field in cancer research. In summary, newly identified lipid regulators of ion channels, such as ELs and PUFAs, may represent valuable targets to improve disease diagnosis and advance the development of new therapeutic strategies for managing a range of diseases and conditions.

PUFA and their derivatives in neurotransmission and synapses: a new hallmark of synaptopathies

PUFA of the n-3 and n-6 families are present in high concentration in the brain where they are major components of cell membranes. The main forms found in the brain are DHA (22 :6, n-3) and arachidonic acid (20:4, n-6). In the past century, several studies pinpointed that modifications of n-3 and n-6 PUFA levels in the brain through dietary supply or genetic means are linked to the alterations of synaptic function. Yet, synaptopathies emerge as a common characteristic of neurodevelopmental disorders, neuropsychiatric diseases and some neurodegenerative diseases. Understanding the mechanisms of action underlying the activity of PUFA at the level of synapses is thus of high interest. In this frame, dietary supplementation in PUFA aiming at restoring or promoting the optimal function of synapses appears as a promising strategy to treat synaptopathies. This paper reviews the link between dietary PUFA, synapse formation and the role of PUFA and their metabolites in synaptic functions.

Cytosolic increased labile Zn2+ contributes to arrhythmogenic action potentials in left ventricular cardiomyocytes through protein thiol oxidation and cellular ATP depletion

Intracellular labile (free) Zn²⁺-level ([Zn²⁺]_i) is low and increases markedly under pathophysiological conditions in cardiomyocytes. High [Zn²⁺]_i is associated with alterations in excitability and ionic-conductances while exact mechanisms are not clarified yet. Therefore, we examined the elevated-[Zn²⁺]_i on some sarcolemmal ionic-mechanisms, which can mediate cardiomyocyte dysfunction. High-[Zn²⁺]_i induced significant changes in action potential (AP) parameters, including depolarization in resting membrane-potential and prolongations in AP-repolarizing phases. We detected also the time-dependent effects such as induction of spontaneous APs at the time of ≥ 3 min following [Zn²⁺]_i increases, a manner of cellular ATP dependent and reversible with disulfide-reducing agent dithiothreitol, DTT. High-[Zn²⁺]_i induced inhibitions in voltage-dependent K⁺-channel currents, such as transient outward K⁺-currents, I_to, steady-state currents, I_ss and inward-rectifier K⁺-currents, I_K1, reversible with DTT seemed to be responsible from the prolongations in APs. We, for the first time, demonstrated that lowering cellular ATP level induced significant decreaeses in both I_ss and I_K1, while no effect on I_to. However, the increased-[Zn²⁺]_i could induce marked activation in ATP-sensitive K⁺-channel currents, I_KATP, depending on low cellular ATP and thiol-oxidation levels of these channels. The mRNA levels of Kv4.3, Kv1.4 and Kv2.1 were depressed markedly with increased-[Zn²⁺]_i with no change in mRNA level of Kv4.2, while the mRNA level of I_KATP subunit, SUR2A was increased significantly with increased-[Zn²⁺]_i, being reversible with DTT. Overall we demonstrated that high-[Zn²⁺]_i, even if nanomolar levels, alters cardiac function via prolonged APs of cardiomyocytes, at most, due to inhibitions in voltage-dependent K⁺-currents, although activation of I_KATP is playing cardioprotective role, through some biochemical changes in cellular ATP- and thiol-oxidation levels. It seems, a well-controlled [Zn²⁺]_i can be novel therapeutic target for cardiac complications under pathological conditions including oxidative stress.

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

Polyunsaturated fatty acids (PUFAs) act on most ion channels, thereby having significant physiological and pharmacological effects. In this review we summarize data from numerous PUFAs on voltage-gated ion channels containing one or several voltage-sensor domains, such as voltage-gated sodium (Na_V), potassium (K_V), calcium (Ca_V), and proton (H_V) channels, as well as calcium-activated potassium (K_Ca), and transient receptor potential (TRP) channels. Some effects of fatty acids appear to be channel specific, whereas others seem to be more general. Common features for the fatty acids to act on the ion channels are at least two double bonds in cis geometry and a charged carboxyl group. In total we identify and label five different sites for the PUFAs. PUFA site 1: The intracellular cavity. Binding of PUFA reduces the current, sometimes as a time-dependent block, inducing an apparent inactivation. PUFA site 2: The extracellular entrance to the pore. Binding leads to a block of the channel. PUFA site 3: The intracellular gate. Binding to this site can bend the gate open and increase the current. PUFA site 4: The interface between the extracellular leaflet of the lipid bilayer and the voltage-sensor domain. Binding to this site leads to an opening of the channel via an electrostatic attraction between the negatively charged PUFA and the positively charged voltage sensor. PUFA site 5: The interface between the extracellular leaflet of the lipid bilayer and the pore domain. Binding to this site affects slow inactivation. This mapping of functional PUFA sites can form the basis for physiological and pharmacological modifications of voltage-gated ion channels.

Polyunsaturated fatty acids inhibit Kv1.4 by interacting with positively charged extracellular pore residues

Polyunsaturated fatty acids (PUFAs) modulate voltage-gated K(+) channel inactivation by an unknown site and mechanism. The effects of ω-6 and ω-3 PUFAs were investigated on the heterologously expressed Kv1.4 channel. PUFAs inhibited wild-type Kv1.4 during repetitive pulsing as a result of slowing of recovery from inactivation. In a mutant Kv1.4 channel lacking N-type inactivation, PUFAs reversibly enhanced C-type inactivation (Kd, 15-43 μM). C-type inactivation was affected by extracellular H(+) and K(+) as well as PUFAs and there was an interaction among the three: the effect of PUFAs was reversed during acidosis and abolished on raising K(+) Replacement of two positively charged residues in the extracellular pore (H508 and K532) abolished the effects of the PUFAs (and extracellular H(+) and K(+)) on C-type inactivation but had no effect on the lipoelectric modulation of voltage sensor activation, suggesting two separable interaction sites/mechanisms of action of PUFAs. Charge calculations suggest that the acidic head group of the PUFAs raises the pKa of H508 and this reduces the K(+) occupancy of the selectivity filter, stabilizing the C-type inactivated state.

Kv3 channel assembly, trafficking and activity are regulated by zinc through different binding sites

Zinc, a divalent heavy metal ion and an essential mineral for life, regulates synaptic transmission and neuronal excitability via ion channels. However, its binding sites and regulatory mechanisms are poorly understood. Here, we report that Kv3 channel assembly, localization and activity are regulated by zinc through different binding sites. Local perfusion of zinc reversibly reduced spiking frequency of cultured neurons most likely by suppressing Kv3 channels. Indeed, zinc inhibited Kv3.1 channel activity and slowed activation kinetics, independent of its site in the N-terminal T1 domain. Biochemical assays surprisingly identified a novel zinc-binding site in the Kv3.1 C-terminus, critical for channel activity and axonal targeting, but not for the zinc inhibition. Finally, mutagenesis revealed an important role of the junction between the first transmembrane (TM) segment and the first extracellular loop in sensing zinc. Its mutant enabled fast spiking with relative resistance to the zinc inhibition. Therefore, our studies provide novel mechanistic insights into the multifaceted regulation of Kv3 channel activity and localization by divalent heavy metal ions.

Immunomodulation of microglia by docosahexaenoic acid and eicosapentaenoic acid

PURPOSE OF REVIEW

The omega-3 fatty acids (ω-3 FAs) docosahexaenoic acid and eicosapentaenoic acid are dietary components which have been ascribed many different health benefits. Inflammation is present in, and contributes to, pathological conditions in the central nervous system (CNS). Microglia are the primary cells with immune function in the CNS, and inflammation mediated by activated microglia is present in pathological conditions. In this review, we present and discuss findings on the modulation of microglial activities by ω-3 FAs in vivo as well as in vitro, and propose mechanisms for their effects.

RECENT FINDINGS

The majority of studies show that ω-3 FAs have anti-inflammatory effects on microglia. However, phagocytosis is an activity associated with inflammation and is increased by ω-3 FAs. This can be understood in the light of recent research on the resolution of inflammation. Resolution is induced by proresolving factors, which are metabolites of ω-3 FAs. Proresolving factors are anti-inflammatory and have been shown to increase phagocytosis. Other mechanisms of the anti-inflammatory actions of ω-3 FAs involve the peroxisome proliferator-activated receptor-γ, ω-3 FA incorporation into the cell membrane, and inhibition of ion currents.

SUMMARY

Immunomodulation by ω-3 FAs is mediated by several pathways that are interconnected and is a potential therapy for disorders in the CNS.

Nutritional determinants of cognitive aging and dementia

The objective of this review is to provide an overview of nutritional factors involved in cognitive aging and dementia with a focus on nutrients that are also important in neurocognitive development. Several dietary components were targeted, including antioxidant nutrients, dietary fats and B-vitamins. A critical review of the literature on each nutrient group is presented, beginning with laboratory and animal studies of the underlying biological mechanisms, followed by prospective epidemiological studies and randomised clinical trials. The evidence to date is fairly strong for protective associations of vitamin E from food sources, the n-3 fatty acid, DHA, found in fish, a high ratio of polyunsaturated to saturated fats, and vitamin B12 and folate. Attention to the level of nutrient intake is crucial for interpreting the literature and the inconsistencies across studies. Most of the epidemiological studies that observe associations have sufficient numbers of individuals who have both low and adequate nutrient status. Few of the randomised clinical trials are designed to target participants who have low baseline status before randomising to vitamin supplement treatments, and this may have resulted in negative findings. Post-hoc analyses by some of the trials reveal vitamin effects in individuals with low baseline intakes. The field of diet and dementia is a relatively young area of study. Much further work needs to be done to understand dietary determinants of cognitive aging and diseases. Further, these studies must be particularly focused on the levels of nutrient intake or status that confer optimum or suboptimal brain functioning.

The omega-3 fatty acid-derived neuroprotectin D1 limits hippocampal hyperexcitability and seizure susceptibility in kindling epileptogenesis

PURPOSE

Temporal lobe epilepsy, one of the most common epilepsy syndromes, is characterized by hippocampal hyperexcitability and progressive seizure susceptibility. Omega-3 fatty acids are involved in neuronal excitability and have anticonvulsant properties. We studied the effect of docosahexaenoic acid (DHA) or its derived lipid mediator, neuroprotectin D1 (NPD1, 10R,17S-dihydroxy-docosa-4Z,7Z,11E,13E,15Z,19Z-hexaenoic acid), in evoked seizures using a rapid kindling model of temporal lobe epilepsy.

METHODS

DHA or NPD1 was administered in rodents with or without kindling acquisition. Locomotor seizures and evoked epileptiform hippocampal activity immediately after hippocampal stimulations were analyzed.

KEY FINDINGS

DHA or NPD1 limits hippocampal electrically induced hyperexcitability. Seizures induced by kindling triggered NPD1 synthesis in the hippocampus. Supplying its precursor, DHA, or direct injection of NPD1 into the third ventricle resulted in attenuation of kindling progression and hippocampal hyperexcitability.

SIGNIFICANCE

The significance of NPD1 in temporal lobe epilepsy could open new pathways for understanding the initiation and propagation of seizures and the role this lipid mediator plays in the neuronal network.

Effects of docosahexaenoic acid on large-conductance Ca2+-activated K+ channels and voltage-dependent K+ channels in rat coronary artery smooth muscle cells

AIM

To investigate the effects of docosahexaenoic acid (DHA) on large-conductance Ca(2+)-activated K(+)(BK(Ca)) channels and voltage-dependent K(+) (K(V)) channels in rat coronary artery smooth muscle cells (CASMCs).

METHODS

Rat CASMCs were isolated by an enzyme digestion method. BK(Ca) and K(V) currents in individual CASMCs were recorded by the patch-clamp technique in a whole-cell configuration at room temperature. Effects of DHA on BK(Ca) and K(V) channels were observed when it was applied at 10, 20, 30, 40, 50, 60, 70, and 80 micromol/L.

RESULTS

When DHA concentrations were greater than 10 micromol/L, BK(Ca) currents increased in a dose-dependent manner. At a testing potential of +80 mV, 6.1%+/-0.3%, 76.5%+/-3.8%, 120.6%+/-5.5%, 248.0%+/-12.3%, 348.7%+/-17.3%, 374.2%+/-18.7%, 432.2%+/-21.6%, and 443.1%+/-22.1% of BK(Ca) currents were increased at the above concentrations, respectively. The half-effective concentration (EC(50)) of DHA on BK(Ca) currents was 37.53+/-1.65 micromol/L. When DHA concentrations were greater than 20 micromol/L, K(V) currents were gradually blocked by increasing concentrations of DHA. At a testing potential of +50 mV, 0.40%+/-0.02%, 1.37%+/-0.06%, 11.80%+/-0.59%, 26.50%+/-1.75%, 56.50%+/-2.89%, 73.30%+/-3.66%, 79.70%+/-3.94%, and 78.1%+/-3.91% of K(V) currents were blocked at the different concentrations listed above, respectively. The EC(50) of DHA on K(V) currents was 44.20+/-0.63 micromol/L.

CONCLUSION

DHA can activate BK(Ca) channels and block K(V) channels in rat CASMCs, and the EC(50) of DHA for BK(Ca) channels is lower than that for K(V) channels; these findings indicate that the vasorelaxation effects of DHA on vascular smooth muscle cells are mainly due to its activation of BK(Ca) channels.

Structure, function, and modification of the voltage sensor in voltage-gated ion channels

Voltage-gated ion channels are crucial for both neuronal and cardiac excitability. Decades of research have begun to unravel the intriguing machinery behind voltage sensitivity. Although the details regarding the arrangement and movement in the voltage-sensor domain are still debated, consensus is slowly emerging. There are three competing conceptual models: the helical-screw, the transporter, and the paddle model. In this review we explore the structure of the activated voltage-sensor domain based on the recent X-ray structure of a chimera between Kv1.2 and Kv2.1. We also present a model for the closed state. From this we conclude that upon depolarization the voltage sensor S4 moves approximately 13 A outwards and rotates approximately 180 degrees, thus consistent with the helical-screw model. S4 also moves relative to S3b which is not consistent with the paddle model. One interesting feature of the voltage sensor is that it partially faces the lipid bilayer and therefore can interact both with the membrane itself and with physiological and pharmacological molecules reaching the channel from the membrane. This type of channel modulation is discussed together with other mechanisms for how voltage-sensitivity is modified. Small effects on voltage-sensitivity can have profound effects on excitability. Therefore, medical drugs designed to alter the voltage dependence offer an interesting way to regulate excitability.

Polyunsaturated fatty acid modulation of voltage-gated ion channels

Arachidonic acid (AA) was found to inhibit the function of whole-cell voltage-gated (VG) calcium currents nearly 16 years ago. There are now numerous examples demonstrating that AA and other polyunsaturated fatty acids (PUFAs) modulate the function of VG ion channels, primarily in neurons and muscle cells. We will review and extract some common features about the modulation by PUFAs of VG calcium, sodium, and potassium channels and discuss the impact of this modulation on the excitability of neurons and cardiac myocytes. We will describe the fatty acid nature of the membrane, how fatty acids become available to function as modulators of VG channels, and the physiologic importance of this type of modulation. We will review the evidence for molecular mechanisms and assess our current understanding of the structural basis for modulation. With guidance from research on the structure of fatty acid binding proteins, the role of lipids in gating mechanosensitive (MS) channels, and the impact of membrane lipid composition on membrane-embedded proteins, we will highlight some avenues for future investigations.

Amino acid substitutions in the pore helix of GluR6 control inhibition by membrane fatty acids

RNA editing at the Q/R site in the GluR5 and GluR6 subunits of neuronal kainate receptors regulates channel inhibition by lipid-derived modulators including the cis-unsaturated fatty acids arachidonic acid and docosahexaenoic acid. Kainate receptor channels in which all of the subunits are in the edited (R) form exhibit strong inhibition by these compounds, whereas wild-type receptors that include a glutamine (Q) at the Q/R site in one or more subunits are resistant to inhibition. In the present study, we have performed an arginine scan of residues in the pore loop of the GluR6(Q) subunit. Amino acids within the range from -19 to +7 of the Q/R site of GluR6(Q) were individually mutated to arginine and the mutant cDNAs were expressed as homomeric channels in HEK 293 cells. All but one of the single arginine substitution mutants yielded functional channels. Only weak inhibition, typical of wild-type GluR6(Q) channels, was observed for substitutions +1 to +6 downstream of the Q/R site. However, arginine substitution at several locations upstream of the Q/R site resulted in homomeric channels exhibiting strong inhibition by fatty acids, which is characteristic of homomeric GluR6(R) channels. Based on homology with the pore loop of potassium channels, locations at which R substitution induces susceptibility to fatty acid inhibition face away from the cytoplasm toward the M1 and M3 helices and surrounding lipids.

Lipoelectric modification of ion channel voltage gating by polyunsaturated fatty acids

Polyunsaturated fatty acids (PUFAs) have beneficial effects on epileptic seizures and cardiac arrhythmia. We report that omega-3 and omega-6 all-cis-PUFAs affected the voltage dependence of the Shaker K channel by shifting the conductance versus voltage and the gating charge versus voltage curves in negative direction along the voltage axis. Uncharged methyl esters of the PUFAs did not affect the voltage dependence, whereas changes of pH and charge mutations on the channel surface affected the size of the shifts. This suggests an electrostatic effect on the channel's voltage sensors. Monounsaturated and saturated fatty acids, as well as trans-PUFAs did not affect the voltage dependence. This suggests that fatty acid tails with two or more cis double bonds are required to place the negative carboxylate charge of the PUFA in a position to affect the channel's voltage dependence. We propose that charged lipophilic compounds could play a role in regulating neuronal excitability by electrostatically affecting the channel's voltage sensor. We believe this provides a new approach for pharmacological treatment that is voltage sensor pharmacology.

Towards a nutritional approach for prevention of Alzheimer's disease: Biochemical and cellular aspects

Alzheimer's disease (AD) is a major public health concern in all countries. Although the precise cause of AD is still unknown, a growing body of evidence supports the notion that soluble amyloid beta-peptide (Abeta) may be the proximate cause of synaptic injuries and neuronal death early in the disease. AD patients display lower levels of docosahexaenoic acid (DHA, C22:6 ; n-3) in plasma and brain tissues as compared to age-matched controls. Furthermore, epidemiological studies suggest that high DHA intake might have protective properties against neurodegenerative diseases. These observations are supported by in vivo studies showing that DHA-rich diets limits the synaptic loss and cognitive defects induced by Abeta peptide. Although the molecular basis of these neuroprotective effects remains unknown, several mechanisms have been proposed such as (i) regulation of the expression of potentially protective genes, (ii) activation of anti-inflammatory pathways, (iii) modulation of functional properties of the synaptic membranes along with changes in their physicochemical and structural features.

Existence of lipid microdomains in bilayer of dipalmitoyl phosphatidylcholine (DPPC) and 1-stearoyl-2-docosahexenoyl phosphatidylserine (SDPS) and their perturbation by chlorpromazine : A 13C and 31P solid-state NMR study

The polyunsaturated fatty acid docosahexaenoic acid (DHA, 22:6, n-3) is found at a level of about 50% in the phospholipids of neuronal tissue membranes and appears to be crucial to human health. Dipalmitoyl phosphatidylcholine (DPPC, 16:0/16:0 PC) and the DHA containing 1-stearoyl-2-docosahexenoyl phosphatidylserine (SDPS) were used to make DPPC (60%)/SDPS (40%) bilayers with and without 10 mol% chlorpromazine (CPZ), a cationic, amphiphilic phenothiazine. Resonances that are present in 13C NMR spectrum of the DPPC (60%)/SDPS (40%) sample and that disappear in presence of 10% CPZ most probably are due to the special interface environment, e.g. the hydrophobic mismatch, at the interface of DPPC and SDPS microdomains in the DPPC/SDPS bilayer. In itself the appearance of resonances at novel chemical shift values is a clear demonstration of a unique chemical environment in the DPPC (60%)/SDPS (40%) bilayer. The findings of the study presented here suggest CPZ bound to the phosphate of SDPS will slow down and partially inhibit such a DHA acyl chain movement in the DPPC/SDPS bilayer. This would affect the area occupied by a SDPS molecule (in the bilayer) and probably the thickness of the bilayer where SDPS molecules reside as well. It is quite likely that such CPZ caused changes can affect the function of proteins embedded in the bilayer.

Q/R site editing controls kainate receptor inhibition by membrane fatty acids

RNA editing within the pore loop controls the pharmacology and permeation properties of ion channels formed by neuronal AMPA and kainate receptor subunits. Genomic sequences for the glutamate receptor 2 (GluR2) subunit of AMPA receptors and the GluR5 and GluR6 subunits of kainate receptors all encode a neutral glutamine (Q) residue within the channel pore that can be converted by RNA editing to a positively charged arginine (R). Receptors comprised of unedited subunits are permeable to calcium and display inwardly rectifying current-voltage relationships, because of blocking of outward current by intracellular polyamines. In contrast, receptors that include edited subunits conduct less calcium, resist polyamine block, and have relatively linear current-voltage relationships. We showed previously that cis-unsaturated fatty acids, including arachidonic acid and docosahexanoic acid, exert a potent block of native kainate receptors as well as homomeric recombinant receptors formed by transfection of heterologous cells with cDNA for the GluR6(R) subunit. Here, we show that fatty acid blockade of recombinant homomeric and heteromeric kainate receptors is strongly dependent on editing at the Q/R site. Recombinant channels that include unedited subunits exhibit significantly weaker block than channels made up of fully edited subunits. Inhibition of fully edited channels is equivalent at voltages from -70 to +40 mV and is noncompetitive, consistent with allosteric regulation of channel function.

Zinc and copper: pharmacological probes and endogenous modulators of neuronal excitability

As well as being key structural components of many proteins, increasing evidence suggests that zinc and copper ions function as signaling molecules in the nervous system and are released from the synaptic terminals of certain neurons. In this review, we consider the actions of these two ions on proteins that regulate neuronal excitability. In addition to the established actions of zinc, and to a lesser degree copper, on excitatory and inhibitory ligand-gated ion channels, we show that both ions have a number of actions on selected members of the voltage-gated-like ion channel superfamily. For example, zinc is a much more effective blocker of one subtype of tetrodotoxin (TTX)-insensitive sodium (Na+) channel (NaV1.5) than other Na+ channels, whereas a certain T-type calcium (Ca2+) channel subunit (CaV3.2) is particularly sensitive to zinc. For potassium (K+) channels, zinc can have profound effects on the gating of certain KV channels whereas zinc and copper have distinct actions on closely related members of the 2 pore domain potassium channel (K2P) channel family. In addition to direct actions on these proteins, zinc is able to permeate a number of membrane proteins such as (S)-alpha-amino-3-hydroxy-5-methyl-4-isoxazole propionic acid (AMPA)/kainate receptors, Ca2+ channels and some transient receptor potential (trp) channels. There are a number of important physiological and pathophysiological consequences of these many actions of zinc and copper on membrane proteins, in terms of regulation of neuronal excitability and neurotoxicity. Furthermore, the concentration of free zinc and copper either in the synaptic cleft or neuronal cytoplasm may contribute to the etiology of certain disease states such as Alzheimer's disease (AD) and epilepsy.

Docosahexaenoic acid: membrane properties of a unique fatty acid

Docosahexaenoic acid (DHA) with 22-carbons and 6 double bonds is the extreme example of an omega-3 polyunsaturated fatty acid (PUFA). DHA has strong medical implications since its dietary presence has been positively linked to the prevention of numerous human afflictions including cancer and heart disease. The PUFA, moreover, is essential to neurological function. It is remarkable that one simple molecule has been reported to affect so many seemingly unrelated biological processes. Although details of a molecular mode of action remain elusive, DHA must be acting at a fundamental level common to many tissues that is related to the high degree of conformational flexibility that the multiple double bonds have been identified to confer. One likely target for DHA action is at the cell membrane where the fatty acid is known to readily incorporate into membrane phospholipids. Once esterified into phospholipids DHA has been demonstrated to significantly alter many basic properties of membranes including acyl chain order and "fluidity", phase behavior, elastic compressibility, permeability, fusion, flip-flop and protein activity. It is concluded that DHA's interaction with other membrane lipids, particularly cholesterol, may play a prominent role in modulating the local structure and function of cell membranes.

Effects of polyunsaturated fatty acids on voltage-gated K+ and Na+ channels in rat olfactory receptor neurons

Although the polyunsaturated fatty acids arachidonic acid (AA) and docosahexaenoic acid (DHA) are enriched in the olfactory mucosa, their possible contribution to olfactory transduction has not been investigated. This study characterized their effects on voltage-gated K+ and Na+ channels of rat olfactory receptor neurons. Physiological (3-10 microm) concentrations of AA and DHA potently and irreversibly inhibited the voltage-gated K+ current in a voltage-independent manner. In addition, both compounds significantly reduced the inhibitory potency of the odorants acetophenone and amyl acetate at these channels. By comparison, the steady-state effects of both AA and DHA on the voltage-gated Na+ channel were relatively weak, with half-maximal inhibition requiring approximately 35 microm of either compound. However, a surprising finding was that the initial application of 3 microm AA to a naïve neuron caused a strong but transient inhibition of the Na+ current. The channels became almost completely resistant to this inhibition within 1 min, and a 2-min wash in control solution was insufficient to restore the strong inhibitory effect. These observations suggest that polyunsaturated fatty acids have the potential to strongly influence the coding of odorant information by olfactory receptor neurons.

Resolvins: a family of bioactive products of omega-3 fatty acid transformation circuits initiated by aspirin treatment that counter proinflammation signals

Aspirin (ASA) is unique among current therapies because it acetylates cyclooxygenase (COX)-2 enabling the biosynthesis of R-containing precursors of endogenous antiinflammatory mediators. Here, we report that lipidomic analysis of exudates obtained in the resolution phase from mice treated with ASA and docosahexaenoic acid (DHA) (C22:6) produce a novel family of bioactive 17R-hydroxy-containing di- and tri-hydroxy-docosanoids termed resolvins. Murine brain treated with aspirin produced endogenous 17R-hydroxydocosahexaenoic acid as did human microglial cells. Human COX-2 converted DHA to 13-hydroxy-DHA that switched with ASA to 17R-HDHA that also proved a major route in hypoxic endothelial cells. Human neutrophils transformed COX-2-ASA-derived 17R-hydroxy-DHA into two sets of novel di- and trihydroxy products; one initiated via oxygenation at carbon 7 and the other at carbon 4. These compounds inhibited (IC(50) approximately 50 pM) microglial cell cytokine expression and in vivo dermal inflammation and peritonitis at ng doses, reducing 40-80% leukocytic exudates. These results indicate that exudates, vascular, leukocytes and neural cells treated with aspirin convert DHA to novel 17R-hydroxy series of docosanoids that are potent regulators. These biosynthetic pathways utilize omega-3 DHA and EPA during multicellular events in resolution to produce a family of protective compounds, i.e., resolvins, that enhance proresolution status.

Linoleic acid both enhances activation and blocks Kv1.5 and Kv2.1 channels by two separate mechanisms

Linoleic acid (LA) had two effects on human Kv1.5 and Kv2.1 channels expressed in Chinese hamster ovary cells: an increase in the speed of current activation process (EC(50) = 2.4 and 2.7 microM for Kv1.5 and Kv2.1, respectively) and current inhibition (IC(50) = 6.6 and 7.4 for Kv1.5 and Kv2.1, respectively). LA affected the activation kinetics via two processes: a leftward shift in the instantaneous activation curves and an increase in the rate of current rise. Current inhibition by LA was time dependent but voltage independent. Hill slopes for plots of current inhibition (3.5 and 3.9 for Kv1.5 and Kv2.1, respectively) vs. dose of LA suggested that cooperativity was involved in the mechanism of current inhibition. A similar analysis of the effects of LA on current activation did not reveal cooperative interactions. The effects of LA were mediated from the external side of the channels, since addition of 10 microM LA to the patch pipette solution was without effect. Additionally, the methyl ester of LA was effective at enhancing peak current and promoting channel activation for Kv1.5 and Kv2.1 without inducing significant current inhibition.

Mechanisms of action of docosahexaenoic acid in the nervous system

This review describes (from both the animal and human literature) the biological consequences of losses in nervous system docosahexaenoate (DHA). It then concentrates on biological mechanisms that may serve to explain changes in brain and retinal function. Brief consideration is given to actions of DHA as a nonesterified fatty acid and as a docosanoid or other bioactive molecule. The role of DHA-phospholipids in regulating G-protein signaling is presented in the context of studies with rhodopsin. It is clear that the visual pigment responds to the degree of unsaturation of the membrane lipids. At the cell biological level, DHA is shown to have a protective role in a cell culture model of apoptosis in relation to its effects in increasing cellular phosphatidylserine (PS); also, the loss of DHA leads to a loss in PS. Thus, through its effects on PS, DHA may play an important role in the regulation of cell signaling and in cell proliferation. Finally, progress has been made recently in nuclear magnetic resonance studies to delineate differences in molecular structure and order in biomembranes due to subtle changes in the degree of phospholipid unsaturation.

A common inhibitory binding site for zinc and odorants at the voltage-gated K(+) channel of rat olfactory receptor neurons

This study compared the effects of zinc and odorants on the voltage-gated K(+) channel of rat olfactory neurons. Zinc reduced current magnitude, depolarized the voltage activation curve and slowed activation kinetics without affecting inactivation or deactivation kinetics. Zinc inhibition was potentiated by the NO compound, S-nitroso-cysteine. The pH- and diethylpyrocarbonate-dependence of zinc inhibition suggested that zinc acted by binding to histidine residues. Cysteine residues were eliminated as contributing to the zinc-binding site. The odorants, acetophenone and amyl acetate, also reduced current magnitude, depolarized the voltage activation curve and selectively slowed activation kinetics. Furthermore, the diethylpyrocarbonate- and pH-dependence of odorant inhibition implied that the odorants also bind to histidine residues. Zinc inhibitory potency was dramatically diminished in the presence of odorants, implying competition for a common binding site. These observations indicate that the odorants and zinc share a common inhibitory binding site on the external surface of the voltage-gated K(+) channel.

Modulation of Kv1.5 potassium channel gating by extracellular zinc

Zinc ions are known to induce a variable depolarizing shift of the ionic current half-activation potential and substantially slow the activation kinetics of most K(+) channels. In Kv1.5, Zn(2+) also reduces ionic current, and this is relieved by increasing the external K(+) or Cs(+) concentration. Here we have investigated the actions of Zn(2+) on the gating currents of Kv1.5 channels expressed in HEK cells. Zn(2+) shifted the midpoint of the charge-voltage (Q-V) curve substantially more (approximately 2 times) than it shifted the V(1/2) of the g-V curve, and this amounted to +60 mV at 1 mM Zn(2+). Both Q1 and Q2 activation charge components were similarly affected by Zn(2+), which indicated free access of Zn(2+) to channel closed states. The maximal charge movement was also reduced by 1 mM Zn(2+) by approximately 15%, from 1.6 +/- 0.5 to 1.4 +/- 0.47 pC (n = 4). Addition of external K(+) or Cs(+), which relieved the Zn(2+)-induced ionic current reduction, decreased the extent of the Zn(2+)-induced Q-V shift. In 135 mM extracellular Cs(+), 200 microM Zn(2+) reduced ionic current by only 8 +/- 1%, compared with 71% reduction in 0 mM extracellular Cs(+), and caused a comparable shift in both the g-V and Q-V relations (17.9 +/- 0.6 mV vs. 20.8 +/- 2.1 mV, n = 6). Our results confirm the presence of two independent binding sites involved in the Zn(2+) actions. Whereas binding to one site accounts for reduction of current and binding to the other site accounts for the gating shift in ionic current recordings, both sites contribute to the Zn(2+)-induced Q-V shift.

External K(+) relieves the block but not the gating shift caused by Zn(2+) in human Kv1.5 potassium channels

1. We used the whole-cell recording technique to examine the effect of extracellular Zn(2+) on macroscopic currents due to Kv1.5 channels expressed in the human embryonic kidney cell line HEK293. 2. Fits of a Boltzmann function to tail current amplitudes showed that 1 mM Zn2+ shifted the half-activation voltage from -10.2 +/- 0.4 to 21.1 +/- 0.7 mV and the slope factor increased from 6.8 +/- 0.4 to 9.4 +/- 0.7 mV. The maximum conductance in 1 mM Zn2+ and with 3.5 mM K(+)o was 33 +/- 7 % of the control value. 3. In physiological saline the apparent KD for the Zn(2+) block was 650 +/- 24 M and was voltage independent. A Hill coefficient of 1.0 +/- 0.03 implied that block is mediated by the occupation of a single binding site. 4. Increasing the external concentration of K(+) ([K(+)]o) inhibited the block by Zn(2+). Estimates of the apparent K(D) of the Zn(2+) block in 0, 5 and 135 mM K(+) were 69, 650 and 2100 M, respectively. External Cs(+) relieved the Zn(2+) block but was less effective than K(+). Changing [K(+)]o did not affect the Zn(2+)-induced gating shift. 5. A model of allosteric inhibition fitted to the relationship between the block by Zn(2+) and the block relief by external K(+) gave KD estimates of approximately 70 M for Zn(2+) and approximately 500 M for K(+). 6. We propose that the gating shift and the block caused by Zn(2+) are mediated by two distinct sites and that the blocking site is located in the external mouth of the pore.

Eicosatetraynoic acid (ETYA), a non-metabolizable analogue of arachidonic acid, blocks the fast-inactivating potassium current of rat pituitary melanotrophs

The effects of arachidonic acid (5,8,11,14-eicosatetraenoic acid, AA) and 5,8,11,14-eicosatetraynoic acid (ETYA), a non-metabolizable analogue of AA, were examined on the transient [IK(f)] and the delayed rectifier-like [IK(s)] voltage-gated potassium currents in rat pituitary melanotrophs. The main questions addressed were whether AA and ETYA blocked IK(f) and if any blocking action was specific. Macroscopic currents were measured using the patch clamp technique. Bath application of 20 µM AA reduced IK(f), however, the degree of the block varied between cells. In contrast, ETYA consistently inhibited IK(f). Fitting of the charge transfer or the peak current amplitude yielded KD estimates for ETYA of 1.2 µM and 3.3 µM, respectively. The reduction by ETYA of peak IK(f) was always associated with an increased rate of current decay, but there was no detectable change of the kinetics of activation. ETYA caused a small left shift of the IK(f) steady-state inactivation curve and significantly slowed recovery from inactivation. At 20 µM, ETYA also reduced IK(s), indicating that it is not specific. The possibility that ETYA acts as an open-channel blocker is discussed.Key words: transient potassium current, melanotroph, eicosatetraynoic acid, ETYA, arachidonic acid.

Antioxidants and fatty acids in the amelioration of rheumatoid arthritis and related disorders

The generation of reactive oxygen species (free radicals) is an important factor in the development and maintenance of rheumatoid arthritis in humans and animal models. One source of free radicals is nitric oxide produced within the synoviocytes and chondrocytes and giving rise to the highly toxic radical peroxynitrite. Several cytokines, including tumour necrosis factor-alpha (TNFalpha) are involved in the formation of free radicals, partly by increasing the activity of nitric oxide synthase. Indeed, nitric oxide may mediate some of the deleterious effects of cytokines on bone resorption. Aspirin, tetracyclines, steroids and methotrexate can suppress nitric oxide synthase. Dietary antioxidants include ascorbate and the tocopherols and beneficial effects of high doses have been reported especially in osteoarthritis. There is also evidence for beneficial effects of beta-carotene and selenium, the latter being a component of the antioxidant enzyme glutathione peroxidase. The polyunsaturated fatty acids (PUFA) include the n-3 compounds, some of which are precursors of eicosanoid synthesis, and the n-6 group which can increase formation of the pro-inflammatory cytokines TNFalpha and interleukin-6, and of reactive oxygen species. Some prostaglandins, however, suppress cytokine formation, so that n-3 PUFA often oppose the inflammatory effects of some n-6-PUFA. gamma-linolenic acid (GLA) is a precursor of prostaglandin E1, a fact which may account for its reported ability to ameliorate arthritic symptoms. Fish oil supplements, rich in n-3 PUFA such as eicosapentaenoic acid have been claimed as beneficial in rheumatoid arthritis, possibly by suppression of the immune system and its cytokine repertoire. Some other oils of marine origin (e.g. from the green-lipped mussel) and a range of vegetable oils (e.g. olive oil and evening primrose oil) have indirect anti-inflammatory actions, probably mediated via prostaglandin E1. Overall, there is a growing scientific rationale for the use of dietary supplements as adjuncts in the treatment of inflammatory disorders such as rheumatoid arthritis and osteoarthritis.

Docosahexaenoic acid inhibits synaptic transmission and epileptiform activity in the rat hippocampus

Docosahexaenoic acid (DHA) has been suggested to be required for neuronal development and synaptic plasticity. However, in view of the fact that DHA facilitates NMDA responses and blocks K(+) channels, it might predispose the neurons to epileptiform bursting. By using extracellular recording of population spikes in the CA1 region of rat hippocampal slices, we tested this possibility by examining the effect of DHA on the epileptiform activity induced by bicuculline or in Mg(2+)-free medium. When stimuli were delivered to the Schaffer collateral/commissural pathway every 20 or 30 sec, DHA had no significant effect on the epileptiform activity. However, when the frequency of stimulation was increased to 0.2 Hz, DHA attenuated the amplitude of the bursting activity induced by bicuculline to 57.5+/- 10.8% and those induced by Mg(2+)-free ACSF to 65.8+/-13.9% of control. DHA reduced the slope of field excitatory postsynaptic potential (fEPSP) to 77.1+/-7.4% of baseline, without significant effect on the ratio of paired-pulse facilitation (PPF). By intracellular recording of neurons in the stratum pyramidale of rat hippocampal slices, we found that DHA markedly inhibited the repetitive firing of action potentials elicited by depolarizing current pulses but did not affect the initial action potential. Thus, DHA may attenuate epileptic activity mainly through the frequency-dependent blockade of Na(+) channels.

Bidirectional actions of docosahexaenoic acid on hippocampal neurotransmissions in vivo

Docosahexaenoic acid (DHA), a 22-carbon fatty acid with six double bonds, is one of the major polyunsaturated fatty acids in fish oils or in the mammalian central nervous system and is believed to be essential for neuronal plasticity and development. In the present study, we evaluated the effect of DHA on hippocampal neurotransmissions using anesthetized rats. Field excitatory postsynaptic potential (fEPSP) evoked by stimulation of the Schaffer collaterals was recorded from the CA1 stratum radiatum. Following intracerebroventricular injection of DHA 25 nmol, the fEPSP slope decreased gradually in 30 min and was eventually suppressed by about 30%. On the other hand, when fEPSP was evoked by stimulation of the perforant path was recorded in the molecular layer of the dentate gyrus, an increase in fEPSP slope occurred over a similar time course after DHA injection. These phenomena were independent of N-methyl-D-aspartate receptor activity. Linoleic acid, one of polyunsaturated fatty acids, was virtually ineffective. Furthermore, we investigated the effect of DHA on hippocampal synaptic plasticity. Although DHA did not alter the profile of paired-pulse facilitation, it inhibited the induction of long-term potentiation in the CA1 area but not in the dentate gyrus. Thus, DHA exerts regionally different effects on hippocampal neurotransmission and may be a good tool for clarifying physiological functions of the hippocampus.

A membrane lipid imbalance plays a role in the phenotypic expression of cystic fibrosis in cftr(-/-) mice

A deficiency in essential fatty acid metabolism has been reported in plasma from patients with cystic fibrosis (CF). However, its etiology and role in the expression of disease is unknown. The objective of this study was to determine whether alterations in fatty acid metabolism are specific to CF-regulated organs and whether they play a role in the expression of disease. A membrane lipid imbalance was found in ileum, pancreas, and lung from cftr(-/-) mice characterized by an increase in phospholipid-bound arachidonic acid and a decrease in phospholipid-bound docosahexaenoic acid (DHA). This lipid imbalance was observed in organs pathologically affected by CF including lung, pancreas, and ileum and was not secondary to impaired intestinal absorption or hepatic biosynthesis of DHA. As proof of concept, oral administration of DHA to cftr(-/-) mice corrected this lipid imbalance and reversed the observed pathological manifestations. These results strongly suggest that certain phenotypic manifestations of CF may result from remediable alterations in phospholipid-bound arachidonic acid and DHA levels.

Health benefits of docosahexaenoic acid (DHA)

Docosahexaenoic acid (DHA) is essential for the growth and functional development of the brain in infants. DHA is also required for maintenance of normal brain function in adults. The inclusion of plentiful DHA in the diet improves learning ability, whereas deficiencies of DHA are associated with deficits in learning. DHA is taken up by the brain in preference to other fatty acids. The turnover of DHA in the brain is very fast, more so than is generally realized. The visual acuity of healthy, full-term, formula-fed infants is increased when their formula includes DHA. During the last 50 years, many infants have been fed formula diets lacking DHA and other omega-3 fatty acids. DHA deficiencies are associated with foetal alcohol syndrome, attention deficit hyperactivity disorder, cystic fibrosis, phenylketonuria, unipolar depression, aggressive hostility, and adrenoleukodystrophy. Decreases in DHA in the brain are associated with cognitive decline during aging and with onset of sporadic Alzheimer disease. The leading cause of death in western nations is cardiovascular disease. Epidemiological studies have shown a strong correlation between fish consumption and reduction in sudden death from myocardial infarction. The reduction is approximately 50% with 200 mg day(-1)of DHA from fish. DHA is the active component in fish. Not only does fish oil reduce triglycerides in the blood and decrease thrombosis, but it also prevents cardiac arrhythmias. The association of DHA deficiency with depression is the reason for the robust positive correlation between depression and myocardial infarction. Patients with cardiovascular disease or Type II diabetes are often advised to adopt a low-fat diet with a high proportion of carbohydrate. A study with women shows that this type of diet increases plasma triglycerides and the severity of Type II diabetes and coronary heart disease. DHA is present in fatty fish (salmon, tuna, mackerel) and mother's milk. DHA is present at low levels in meat and eggs, but is not usually present in infant formulas. EPA, another long-chain n-3 fatty acid, is also present in fatty fish. The shorter chain n-3 fatty acid, alpha-linolenic acid, is not converted very well to DHA in man. These longchain n-3 fatty acids (also known as omega-3 fatty acids) are now becoming available in some foods, especially infant formula and eggs in Europe and Japan. Fish oil decreases the proliferation of tumour cells, whereas arachidonic acid, a longchain n-6 fatty acid, increases their proliferation. These opposite effects are also seen with inflammation, particularly with rheumatoid arthritis, and with asthma. DHA has a positive effect on diseases such as hypertension, arthritis, atherosclerosis, depression, adult-onset diabetes mellitus, myocardial infarction, thrombosis, and some cancers.

Cancellation of low-frequency stimulation-induced long-term depression by docosahexaenoic acid in the rat hippocampus

The effects of docosahexaenoic acid (DHA) on low-frequency stimulation (LFS)-induced long-term depression (LTD) were investigated in the CA 1 subfield of rat hippocampal slices. LTD was routinely produced by LFS of 900 pulses at 1 Hz. The field excitatory postsynaptic potential (fEPSP) 40 min after LFS was 59 +/- 4% (n = 18) of baseline response. However, in experiments from 18 neurons pretreated with DHA (50 microM), fEPSP returned to baseline levels within 20 min after LFS in eight cells and was slightly potentiated in three cells. Only in seven cells was LTD induced. The effect of DHA on LTD was concentration dependent. The slopes of fEPSP 40 min after LFS were 67 +/- 4% (n = 6), 72 +/- 7% (n = 7) and 80 +/- 5% (n = 18) of baseline response, with pretreatment of 1, 10 and 50 microM DHA, respectively. The blockade of LTD induction suggests that DHA may play a role in learning and memory.

Pathophysiological effects of dietary essential fatty acid balance on neural systems

Dietary fatty acid balance has been revealed to affect neural functions as well as chronic diseases such as cancer, cerebro- and cardiovascular diseases, and allergic hyper-reactivity. In this review, we focused on the pathophysiological effects of n-6 and n-3 fatty acids on brain functions. Long-term n-3 fatty acid deficiency in the presence of n-6 fatty acids has been shown to affect learning behavior, drug sensitivity and retinal functions. Some membrane enzymes and ion channel functions have been shown in experimental animals to be regulated by membrane fatty acid modifications. We also summarized the effects of these fatty acids in diets on human psychotic aspects and brain diseases. Although biochemical mechanisms remain to be elucidated, investigations on the effect of dietary fatty acids on neural networks may provide an important clue to clarify complex brain functions.

Effects of arachidonic acid on A-type potassium currents in smooth muscle cells of the guinea pig

Effects of arachidonic acid (AA) and related fatty acids on Ca2+ -independent transient (A-type) K+ current (I(A)) were examined in single myocytes of guinea pig vas deferens, ureter, and proximal colon as well as in rabbit vas deferens. The peak amplitude of I(A) was reduced by external application of AA (half-maximal inhibitory concentration = approximately 1 microM). The blocking effect was not changed significantly by indomethacin, nordihydroguaiaretic acid, guanosine 5'-O-(2-thiodiphosphate), or guanosine 5'-O-(3-thiotriphosphate). Pharmacological studies suggested that the effect of AA was not mediated by activation of protein kinases A or C or tyrosine kinase. AA (20:4) was the most potent of the four types of cis-eicosanoic acids with two to five double bonds (20:2 to 20:5) that were tested. I(A)-like current in cardiac atrial myocytes of the rabbit was not affected significantly by 30 microM AA. These results indicate that AA itself directly blocks A-type K+ channels. A relationship between stereospecific chemical structure of fatty acids and their blockade of A-type K+ channels is suggested. A-type K+ channels in smooth muscle cells can be clearly resolved from those in atrial myocytes by the responses to AA.

Anandamide, an endogenous cannabinoid, inhibits Shaker-related voltage-gated K+ channels

Anandamide has been identified in porcine brain as an endogenous cannabinoid receptor ligand and is believed to be a counterpart to the psychoactive component of marijuana, delta 9-tetrahydrocannabinol (delta 9-THC). Here we report that anandamide directly inhibits (IC50, 2.7 muM) Shaker-related Kv1.2 K+ channels that are found ubiquitously in the mammalian brain. Delta 9-THC also inhibited Kv1.2 channels with comparable potency (IC50, 2.4 muM), as did several N-acyl-ethanolamides with cannabinoid receptor binding activity. Potassium current inhibition occurred through a pertussis toxin-insensitive mechanism and was not prevented by the cannabinoid receptor antagonist SR141716A. Utilizing excised patches of Kv1.2 channel-rich membrane as a rapid and sensitive bioassay, we found that phospholipase D stimulated the release of an endogenous anandamide-like K+ channel blocker from rat brain slices. Structure-activity studies were consistent with the possibility that the released blocker was either anandamide or another N-acyl-ethanolamide.

Ciclopirox olamine lotion 1%: bioequivalence to ciclopirox olamine cream 1% and clinical efficacy in tinea pedis

Studies were conducted to assess the bioequivalence of a new antimycotic formulation, ciclopirox olamine lotion 1%, to an established compound, ciclopirox olamine cream 1%. Results of in vitro studies, using skin samples from human cadavers and domestic pigs, demonstrated that the two formulations equally penetrate all layers of the stratum corneum and inhibit the growth of Trichophyton mentagrophytes and Candida albicans. In vivo studies in guinea pigs and in human volunteers demonstrated the comparable therapeutic efficacy of the lotion and the cream in experimental trichophytosis. In addition, a multicenter, double-blind clinical trial was undertaken to compare ciclopirox olamine lotion 1% with the vehicle alone in the treatment of patients with tinea pedis. Patients with plantar, interdigital, or vesicular tinea pedis were enrolled in the studies. Patients were treated for 28 days. Clinical and mycological responses were determined during treatment and two weeks posttreatment. Ciclopirox olamine lotion 1% was found to be significantly more effective than its vehicle in the treatment of patients with common tinea pedis. Minor localized side effects (pruritus, burning sensation) were reported in 2% of 89 patients treated with ciclopirox olamine lotion 1%. The results demonstrate the bioequivalence of ciclopirox olamine lotion 1% and ciclopirox olamine cream 1% and confirm the clinical effectiveness and safety of the lotion in the treatment of tinea pedis, a generally recalcitrant fungal infection. It is concluded that ciclopirox olamine lotion 1% can be used as an alternative to ciclopirox olamine cream 1% for treatment of tinea pedis, tinea versicolor, tinea cruris, tinea corporis, and cutaneous candidiasis when the convenience and/or cosmetic elegance of a lotion is desired.