Kearns-Sayre syndrome: Cerebral folate deficiency,MRI findings and new cerebrospinal fluid biochemical features

We evaluated cerebrospinal fluid (CSF) 5-methyltetrahydrofolate (5-MTHF), biogenic amines, and white matter status in six Kearns-Sayre syndrome (KSS) patients. They presented severe 5-MTHF deficiency. A significant negative correlation was observed between CSF 5-MTHF and protein concentration. CSF homovanillic acid was clearly high. Regarding neuroimaging, the main feature was hyperintensity in the basal ganglia, brainstem, and cerebral/cerebellar white matter. The severity of hemispheric white matter disturbances appeared to be qualitatively associated with 5-MTHF values. The negative correlation between 5-MTHF and proteins supports the hypothesis of impaired choroid plexus function. Interestingly, despite very low 5-MTHF, clearly high neurotransmitter metabolites were found.     

Characterization of folate uptake by choroid plexus epithelial cells in a rat primary culture model

Reduced derivatives of folic acid (folates) play a critical role in the development, function and repair of the CNS. However, the molecular systems regulating folate uptake and homeostasis in the central nervous system remain incompletely defined. Choroid plexus epithelial cells express high levels of folate receptor α (FRα) suggesting that the choroid plays an important role in CNS folate trafficking and maintenance of CSF folate levels. We have characterized 5-methyltetrahydrofolate (5-MTHF) uptake and metabolism by primary rat choroid plexus epithelial cells in vitro . Two distinct processes are apparent; one that is FRα dependent and one that is independent of the receptor. FRα binds 5-MTHF with high affinity and facilitates efficient uptake of 5-MTHF at low extracellular folate concentrations; a lower affinity FRα independent system accounts for increased folate uptake at higher concentrations. Cellular metabolism of 5-MTHF depends on the route of folate entry into the cell. 5-MTHF taken up via a non-FRα -mediated process is rapidly metabolized to folylpolyglutamates, whereas 5-MTHF that accumulates via FRα remains non-metabolized, supporting the hypothesis that FRα may be part of a pathway for transcellular movement of the vitamin. The proton-coupled folate transporter, proton-coupled folate transporter (PCFT), mRNA was also shown to be expressed in choroid plexus epithelial cells. This is consistent with the role we have proposed for proton-coupled folate transporter in FRα-mediated transport as the mechanism of export of folates from the endocytic compartment containing FRα.     

Modulation of the mitochondrial large-conductance calcium-regulated potassium channel by polyunsaturated fatty acids

Polyunsaturated fatty acids (PUFAs) and their metabolites can modulate several biochemical processes in the cell and thus prevent various diseases. PUFAs have a number of cellular targets, including membrane proteins. They can interact with plasma membrane and intracellular potassium channels. The goal of this work was to verify the interaction between PUFAs and the most common and intensively studied mitochondrial large conductance Ca²⁺-regulated potassium channel (mitoBK_Ca). For this purpose human astrocytoma U87 MG cell lines were investigated using a patch-clamp technique. We analyzed the effects of arachidonic acid (AA); eicosatetraynoic acid (ETYA), which is a non-metabolizable analog of AA; docosahexaenoic acid (DHA); and eicosapentaenoic acid (EPA). The open probability (P_o) of the channel did not change significantly after application of 10 μM ETYA. P_o increased, however, after adding 10 μM AA. The application of 30 μM DHA or 10 μM EPA also increased the P_o of the channel. Additionally, the number of open channels in the patch increased in the presence of 30 μM EPA. Collectively, our results indicate that PUFAs regulate the BK_Ca channel from the inner mitochondrial membrane.     

Biochemical parameters to assess choroid plexus dysfunction in Kearns-Sayre syndrome patients

Our aim was to assess biochemical parameters to detect choroid plexus dysfunction in Kearns–Sayre syndrome (KSS) patients. We studied CSF from 7 patients with KSS including total proteins, 5-methyltetrahydrofolate, homovanillic acid (HVA) and Selenium (Se) concentrations. High Se values, increased HVA and total protein concentrations and decreased 5-MTHF values were observed in all cases. This pattern seems very specific to KSS since it was only detected in 7 patients out of 1850 CSF samples analysed, and may represent a good biochemical model for evaluating choroid plexus dysfunction. The accumulated Se in CSF might have deleterious consequences such as toxicity effects.     

Micromolar changes in lysophosphatidylcholine concentration cause minor effects on mitochondrial permeability but major alterations in function

Mice deficient in group 1b phospholipase A₂ have decreased plasma lysophosphatidylcholine and increased hepatic oxidation that is inhibited by intraperitoneal lysophosphatidylcholine injection. This study sought to identify a mechanism for lysophosphatidylcholine-mediated inhibition of hepatic oxidative function. Results showed that in vitro incubation of isolated mitochondria with 40–200 μM lysophosphatidylcholine caused cyclosporine A-resistant swelling in a concentration-dependent manner. However, when mitochondria were challenged with 220 μM CaCl₂, cyclosporine A protected against permeability transition induced by 40 μM, but not 80 μM lysophosphatidylcholine. Incubation with 40–120 μM lysophosphatidylcholine also increased mitochondrial permeability to 75 μM CaCl₂ in a concentration-dependent manner. Interestingly, despite incubation with 80 μM lysophosphatidylcholine, the mitochondrial membrane potential was steady in the presence of succinate, and oxidation rates and respiratory control indices were similar to controls in the presence of succinate, glutamate/malate, and palmitoyl-carnitine. However, mitochondrial oxidation rates were inhibited by 30–50% at 100 μM lysophosphatidylcholine. Finally, while 40 μM lysophosphatidylcholine has no effect on fatty acid oxidation and mitochondria remained impermeable in intact hepatocytes, 100 μM lysophosphatidylcholine inhibited fatty acid stimulated oxidation and caused intracellular mitochondrial permeability. Taken together, these present data demonstrated that LPC concentration dependently modulates mitochondrial microenvironment, with low micromolar concentrations of lysophosphatidylcholine sufficient to change hepatic oxidation rate whereas higher concentrations are required to disrupt mitochondrial integrity.     

The action of n-propyl gallate on gluconeogenesis and oxygen uptake in the rat liver

In the present study the metabolic actions of n-propyl gallate on hepatic gluconeogenesis, oxygen uptake and related parameters were investigated. Experiments were done in the isolated perfused rat liver. n-Propyl gallate inhibited gluconeogenesis and stimulated oxygen uptake at concentrations up to 200 μM. The inhibitory effects on lactate gluconeogenesis (ED₅₀ 86.4 μM) and alanine gluconeogenesis were considerably more pronounced than those on glycerol and fructose gluconeogenesis. n-Propyl gallate also stimulated oxygen uptake in both the mitochondrial (63%) and microsomal (37%) electron transport chains. The first one is due mainly to the oxidation of n-propanol, as a metabolite of the first step of n-propyl gallate transformation. The second one results from a direct stimulation of the microsomal electron transport chain. n-Propyl gallate inhibited pyruvate carboxylation (ED₅₀ 142.2 μM) in consequence of an inhibition of pyruvate transport into the mitochondria an effect not found for gallic acid. This is probably the main cause for glucose output inhibition. Secondary causes are (1) deviation of intermediates for the production of NADPH to be used in microsomal electron transport; (2) deviation of glucose 6-phosphate for glucuronidation reactions; (3) gluconeogenesis inhibition by n-propanol, produced intracellularly from n-propyl gallate. Inhibition of mitochondrial energy metabolism is not significant in the range up to 200 μM, as indicated by the very small effect on the cellular ATP levels (5% decreased). n-Propyl gallate can be considered a kind of metabolic effector, whose actions on the liver metabolism are relatively mild although they can become harmful for the organ and the whole organism at high doses and concentrations.     

High-performance liquid chromatographic assay for the determination of 5-methyltetrahydrofolate in human plasma

An isocratic high-performance liquid chromatographic method for the determination of 5-methyltetrahydrofolate (5-MTHF) in human plasma is described. The method involves solid-phase extraction of 5-MTHF and p-aminoacetophenon (an internal standard) using Sep-Pak C₁₈ cartridges. Separation was achieved with an ODS column using acetonitrile and phosphate buffer supplemented with octanesulfonic acid (an ion-pairing agent). The pH of the mobile phase (2.5) was optimal with respect to the mode of detection (fluorescence). The method was validated in the range of 5-MTHF concentrations from 0.0625 μmol/l to 4.0 μmol/l. Within-day and inter-day precision expressed by the relative standard deviation was less than 8.1% and inaccuracy did not exceed 8.7%. The method is specific, accurate and sensitive enough to be used in pharmacokinetic studies for the assessment of the systemic availability of 5-MTHF after leucovorin administration to patients as a rescue after high-dose therapy with methotrexate. The limit of detection was 0.17 pmol which corresponds to a plasma concentration of 1.7 nmol/l. Thus, the assay could potentially be used for the measurement of 5-MTHF in the range of physiological concentrations in plasma (5–20 nmol/l).     

Effects of taurine and hypotaurine supplementation and ionophore concentrations on post-thaw acrosome reaction of dog spermatozoa

The aim of this work was to study of the effect of the amino acids (AA) taurine (T) and hypotaurine (H) and of different calcium ionophore concentrations on the ability of capacitated frozen-thawed dog sperm to undergo the acrosome reaction (AR). Fifteen ejaculates grouped into five pools were used. Sperm was frozen at a concentration of 80 × 10⁶ sperm cells/mL in the Uppsala Equex extender (UE) supplemented with 25, 50 and 75 mM of either AA. The UE extender without T or H was used as control. After thawing, sperm was capacitated with Canine Capacitation Medium for 20 min. Sperm was then challenged with calcium ionophore A23178 at 0, 2.5 and 10 μM concentration and evaluated for integrity of plasma and acrosome membranes after 5, 15 and 30 min of incubation, utilizing PI/Fitc-PNA fluorescent staining and flow cytometry.Sperm cryopreserved in UE supplemented with 50 mM T (UE 50T) had higher AR rates than sperm cryopreserved with UE 75T, UE 25H and UE 50H, but AR rates were similar to semen frozen with the control extender. Challenges with 2.5 and 10 μM/L of calcium ionophore increased AR in frozen-thawed sperm incubated for 5, 15 and 30 min. The combination of calcium ionophore concentration and incubation time resulting in the highest AR rate was 10 μM and 15 min.     

Intracellular oxidative stress and cytotoxicity in rat primary cortical neurons exposed to cholesterol secoaldehyde

Cholesterol secoaldehyde (ChSeco or 3β-hydroxy-5-oxo-5,6-secocholestan-6-al) has been shown to induce Aβ aggregation and apoptosis in GT1-7 hypothalamic neurons. The present study was undertaken to evaluate the effects of ChSeco on rat primary cortical neuronal cells. ChSeco was cytotoxic at concentrations ranging from 5 to 20 μM, while cholesterol of comparable concentrations showed little or no toxicity. In ChSeco-exposed neuronal cells, there was an increased formation of intracellular peroxide or peroxide-like substance(s), the levels of which were comparable to those found in typical menadione exposures. There was a loss in the mitochondrial transmembrane potential, the extent of which was dependent on concentration of ChSeco employed. Pre-treatment with N-acetyl-l-cysteine (5 mM; 1 h) offered protection against the cytotoxicity and the generation of intracellular oxidants. Cytotoxicity of ChSeco was evidenced by the loss of axonal branches and also condensed apoptotic nuclei in these cells. Immunohistochemical analysis revealed a decreased intracellular Aβ42 staining proportional to the loss in the axonal out growth and dendritic branches. The observed decrease in Aβ42 has been suggested to be due to loss of integrity of dendrites and the plasma membrane, possibly resulting from increased production of reactive oxygen species.     

CISD1 codifies a mitochondrial protein upregulated by the CFTR channel

Cystic fibrosis (CF) is an autosomic recessive disease caused by mutations in the CFTR chloride channel, which indirectly affect the expression of a net of genes. Here we describe a new CFTR-dependent gene, CISD1, encoding for the first member of a family of proteins possessing a CDGSH signature. CISD1 mRNA is down-regulated in cystic fibrosis cells, and restored in the same cells ectopically expressing wt-CFTR (CFDE and CFDE/6RepCFTR; IB3-1 and S9 cells). Inhibition of CFTR chloride transport activity by using glibenclamide (50 μM, 24 h) or CFTR(inh)-172 (5 μM, 24 h), resulted in the down-regulation of CISD1 mRNA, and CFTR stimulation with cAMP/isoproterenol/IBMX upregulated its expression. As predicted by PSORT II, a CISD1-GFP chimera was found to be located into mitochondria, suggesting a possible role in the function/regulation of mitochondrial activity, in agreement with earlier observations of a possible mitochondrial failure in cystic fibrosis.     

Succinimidyl oleate, established inhibitor of CD36/FAT translocase inhibits complex III of mitochondrial respiratory chain

The functional role of CD36 protein detected in mitochondrial fractions in long chain fatty acid (LCFA) oxidation is unclear due to conflicting results obtained in Cd36 knockout mice and experiments using sulfo-N-succinimidyl oleate (SSO) for inhibition of CD36 mediated LCFA transport. We investigated effect of SSO on mitochondrial respiration and found that SSO substantially inhibits not only LCFA oxidation, but also oxidation of flavoprotein- and NADH-dependent substrates and generation of mitochondrial membrane potential. Experiments in rat liver, heart and kidney mitochondria demonstrated a direct effect on mitochondrial respiratory chain with the most pronounced inhibition of the complex III (IC₅₀ 4 μM SSO). The results presented here show that SSO is a potent and irreversible inhibitor of mitochondrial respiratory chain.     

Ammonium uptake kinetics in root and leaf cells of Zostera marina L.

Ammonium uptake rates and the mechanism for ammonium transport into the cells have been analysed in Zostera marina L. In the cells of this species, a proton pump is present in the plasmalemma, which maintains the membrane potential. However, this seagrass shows a high-affinity transport mechanism both for nitrate and phosphate which is dependent on sodium and is unique among angiosperms. We have then analysed if the transport of another N form, ammonium, is also dependent of sodium. First, we have studied ammonium transport at the cellular level by measurements of membrane potentials, both in epidermal root cells and mesophyll cells. And second, we have monitored uptake rates in whole leaves and roots by depletion experiments. The results showed that ammonium is taken up by a high-affinity transport system both in root and leaf cells, although two different of kinetics could be discerned in mesophyll cells (with affinity constants of 2.2 ± 1.1 μM NH₄⁺, in the range 0.01-10 μM NH₄⁺, and 23.2 ± 7.1 μM NH₄⁺, at concentrations between 10 and 500 μM NH₄⁺). However, only one kinetic could be observed in epidermal root cells, which showed a K_m = 11.2 ± 1.0 μM NH₄⁺, considering the whole ammonium concentration range assayed (0.01-500 μM NH₄⁺). The higher affinity of leaf cells for ammonium was consistent with the higher uptake rates observed in leaves, with respect to roots, in depletion experiments at 10 μM NH₄⁺ initial concentration. However, when an initial concentration of 100 μM was assayed, the difference between uptake rates was reduced, but still being higher in leaves. Variations in proton or sodium-electrochemical gradient did not affect ammonium uptake, suggesting that the transport of this nutrient is not driven by these ions and that the ammonium transport mechanism could be different to the transport of nitrate and phosphate in this species.     

N-acetylcysteine, coenzyme Q10 and superoxide dismutase mimetic prevent mitochondrial cell dysfunction and cell death induced by d-galactosamine in primary culture of human hepatocytes

d-Galactosamine (d-GalN) induces reactive oxygen species (ROS) generation and cell death in cultured hepatocytes. The aim of the study was to evaluate the cytoprotective properties of N-acetylcysteine (NAC), coenzyme Q₁₀ (Q₁₀) and the superoxide dismutase (SOD) mimetic against the mitochondrial dysfunction and cell death in d-GalN-treated hepatocytes. Hepatocytes were isolated from liver resections. NAC (0.5 mM), Q₁₀ (30 μM) or MnTBAP (Mn(III)tetrakis(4-benzoic acid) porphyrin chloride (1 mg/mL) were co-administered with d-GalN (40 mM) in hepatocytes. Cell death, oxidative stress, mitochondrial transmembrane potential (MTP), ATP, mitochondrial oxidized/reduced glutathione (GSH) and Q₁₀ ratios, electronic transport chain (ETC) activity, and nuclear- and mitochondria-encoded expression of complex I subunits were determined in hepatocytes. d-GalN induced a transient increase of mitochondrial hyperpolarization and oxidative stress, followed by an increase of oxidized/reduced GSH and Q₁₀ ratios, mitochondrial dysfunction and cell death in hepatocytes. The cytoprotective properties of NAC supplementation were related to a reduction of ROS generation and oxidized/reduced GSH and Q₁₀ ratios, and a recovery of mitochondrial complexes I + III and II + III activities and cellular ATP content. The co-administration of Q₁₀ or MnTBAP recovered oxidized/reduced GSH ratio, and reduced ROS generation, ETC dysfunction and cell death induced by d-GalN. The cytoprotective properties of studied antioxidants were related to an increase of the protein expression of nuclear- and mitochondrial-encoded subunits of complex I. In conclusion, the co-administration of NAC, Q₁₀ and MnTBAP enhanced the expression of complex I subunits, and reduced ROS production, oxidized/reduced GSH ratio, mitochondrial dysfunction and cell death induced by d-GalN in cultured hepatocytes.     

Mitochondrial Ca influx and efflux rates in guinea pig cardiac mitochondria:Low and high affinity effects of cyclosporine A

Ca²⁺ plays a central role in energy supply and demand matching in cardiomyocytes by transmitting changes in excitation-contraction coupling to mitochondrial oxidative phosphorylation. Matrix Ca²⁺ is controlled primarily by the mitochondrial Ca²⁺ uniporter and the mitochondrial Na⁺/Ca²⁺ exchanger, influencing NADH production through Ca²⁺-sensitive dehydrogenases in the Krebs cycle. In addition to the well-accepted role of the Ca²⁺-triggered mitochondrial permeability transition pore in cell death, it has been proposed that the permeability transition pore might also contribute to physiological mitochondrial Ca²⁺ release. Here we selectively measure Ca²⁺ influx rate through the mitochondrial Ca²⁺ uniporter and Ca²⁺ efflux rates through Na⁺-dependent and Na⁺-independent pathways in isolated guinea pig heart mitochondria in the presence or absence of inhibitors of mitochondrial Na⁺/Ca²⁺ exchanger (CGP 37157) or the permeability transition pore (cyclosporine A). cyclosporine A suppressed the negative bioenergetic consequences (ΔΨ_m loss, Ca²⁺ release, NADH oxidation, swelling) of high extramitochondrial Ca²⁺ additions, allowing mitochondria to tolerate total mitochondrial Ca²⁺ loads of > 400 nmol/mg protein. For Ca²⁺ pulses up to 15 μM, Na⁺-independent Ca²⁺ efflux through the permeability transition pore accounted for ~ 5% of the total Ca²⁺ efflux rate compared to that mediated by the mitochondrial Na⁺/Ca²⁺ exchanger (in 5 mM Na⁺). Unexpectedly, we also observed that cyclosporine A inhibited mitochondrial Na⁺/Ca²⁺ exchanger-mediated Ca²⁺ efflux at higher concentrations (IC₅₀ = 2 μM) than those required to inhibit the permeability transition pore, with a maximal inhibition of ~ 40% at 10 μM cyclosporine A, while having no effect on the mitochondrial Ca²⁺ uniporter. The results suggest a possible alternative mechanism by which cyclosporine A could affect mitochondrial Ca²⁺ load in cardiomyocytes, potentially explaining the paradoxical toxic effects of cyclosporine A at high concentrations. This article is part of a Special Issue entitled: Mitochondria and Cardioprotection.     

Single nucleotide polymorphism in CPT1B and CPT2 genes and its association with blood carnitine levels in acute myocardial infarction patients

Ischemic and reperfusion injuries in acute myocardial infarction (AMI) lead to mitochondrial dysfunction in heart cells. Lipid metabolism takes place in mitochondria where carnitine palmitoyltransferase (CPT) enzyme system facilitates the transport of long-chain fatty acids into matrix to provide substrates for beta-oxidation. We sequenced the coding regions of CPT1B and CPT2 genes to identify the single nucleotide polymorphism (SNP) in 23 AMI patients and 23 normal subjects. We also determined blood carnitine levels in these samples to study the impact of these SNPs on carnitine homeostasis. The sequencing of coding regions revealed 4 novel variants in CPT1B gene (G320D, S427C, E531K, and A627E) and 2 variants in CPT2 gene (V368I and M647V). There were significant increases in total carnitine (54.18 ± 3.11 versus 21.49 ± 1.03 μmol/l) and free carnitine (37.78 ± 1.87 versus 10.06 ± 0.80 μmol/l) levels in AMI patients as compared to normal subjects. CPT1B heterozygous variants of G320D and S427C among control subjects showed significantly higher levels of total and free carnitine in the blood. The homozygous genotype (AA) of CPT2 variant V368I had significantly less blood carnitine in AMI patients. Serum troponin T was significantly less in GG genotype of CPT1B variant S427C whereas the genotype AA of CPT2 variant V368I showed significantly higher serum troponin T levels. Further studies on large number of patients are necessary to confirm the role of CPT1B and CPT2 polymorphism in AMI.     

Myoglobin-H2O2 catalyzes the oxidation of β-ketoacids to α-dicarbonyls: mechanism and implications in ketosis

Acetoacetate (AA) and 2-methylacetoacetate (MAA) are accumulated in metabolic disorders such as diabetes and isoleucinemia. Here we examine the mechanism of AA and MAA aerobic oxidation initiated by myoglobin (Mb)/H₂O₂. We propose a chemiluminescent route involving a dioxetanone intermediate whose thermolysis yields triplet α-dicarbonyl species (methylglyoxal and diacetyl). The observed ultraweak chemiluminescence increased linearly on raising the concentration of either Mb (10-500 μM) or AA (10-100 mM). Oxygen uptake studies revealed that MAA is almost a 100-fold more reactive than AA. EPR spin-trapping studies with MNP/MAA revealed the intermediacy of an α-carbon-centered radical and acetyl radical. The latter radical, probably derived from triplet diacetyl, is totally suppressed by sorbate, a well-known quencher of triplet carbonyls. Furthermore, an EPR signal assignable to MNP-AA^• adduct was observed and confirmed by isotope effects. Oxygen consumption and α-dicarbonyl yield were shown to be dependent on AA or MAA concentrations (1-50 mM) and on H₂O₂ or tert-butOOH added to the Mb-containing reaction mixtures. That ferrylMb is involved in a peroxidase cycle acting on the substrates is suggested by the reaction pH profiles and immunospin-trapping experiments. The generation of radicals and triplet dicarbonyl products by Mb/H₂O₂/β-ketoacids may contribute to the adverse health effects of ketogenic unbalance.     

Design,synthesis, and enzyme kinetics of novel benzimidazole and quinoxaline derivatives as methionine synthase inhibitors

Methionine synthase catalyzes the transfer of a methyl group from 5-methyltetrahydrofolate to homocysteine, producing methionine and tetrahydrofolate. Benzimidazole and deazatetrahydrofolates derivatives have been shown to inhibit methionine synthase by competing with the substrate 5-methyltetrahydrofolate. In this study, a novel series of substituted benzimidazoles and quinoxalines were designed and assessed for inhibitory activity against purified rat liver methionine synthase using a radiometric enzyme assay. Compounds 3g, 3j, and 5c showed the highest activity against methionine synthase (IC₅₀: 20 μM, 18 μM, 9 μM, respectively). Kinetic analysis of these compounds using Lineweaver–Burk plots revealed characteristics of mixed inhibition for 3g and 5c; and uncompetitive inhibition for 3j. Docking study into a homology model of the rat methionine synthase gave insights into the molecular determinants of the activity of this class of compounds. The identification of these drug-like inhibitors could lead the design of the next generation modulators of methionine synthase.     

Simultaneous determination of catecholamines, uric acid and ascorbic acid at physiological levels using poly(N-methylpyrrole)/Pd-nanoclusters sensor

An interesting electrochemical sensor has been constructed by the electrodeposition of palladium nanoclusters (Pd_nano) on poly(N-methylpyrrole) (PMPy) film-coated platinum (Pt) electrode. Cyclic voltammetry, electrochemical impedance spectroscopy (EIS), and scanning electron microscopy were used to characterize the properties of the modified electrode. It was demonstrated that the electroactivity of the modified electrode depends strongly on the electrosynthesis conditions of the PMPy film and Pd_nano. Moreover, the modified electrode exhibits strong electrocatalytic activity toward the oxidation of a mixture of dopamine (DA), ascorbic acid (AA), and uric acid (UA) with obvious reduction of overpotentials. The simultaneous analysis of this mixture at conventional (Pt, gold [Au], and glassy carbon) electrodes usually struggles. However, three well-resolved oxidation peaks for AA, DA, and UA with large peak separations allow this modified electrode to individually or simultaneously analyze AA, DA, and UA by using differential pulse voltammetry (DPV) with good stability, sensitivity, and selectivity. This sensor is also ideal for the simultaneous analysis of AA, UA and either of epinephrine (E), norepinephrine (NE) or l-DOPA. Additionally, the sensor shows strong electrocatalytic activity towards acetaminophen (ACOP) and other organic compounds. The calibration curves for AA, DA, and UA were obtained in the ranges of 0.05 to 1 mM, 0.1 to 10 μM, and 0.5 to 20 μM, respectively. The detection limits (signal/noise [S/N] = 3) were 7 μM, 12 nM, and 27 nM for AA, DA, and UA, respectively. The practical application of the modified electrode was demonstrated by measuring the concentrations of AA, DA, and UA in injection sample, human serum, and human urine samples, respectively, with satisfactory results. The reliability and stability of the modified electrode gave a good possibility for applying the technique to routine analysis of AA, DA, and UA in clinical tests.     

Pharmacological characterisation of 5-hydroxytryptamine-induced contractile effects in the isolated gut of the lepidopteran caterpillar Spodoptera frugiperda

The indolealkylamine 5-hydroxytryptamine (5-HT, 0.1 nM-1 μM) caused dose-dependent increases in the number of contractions observed in guts isolated from the caterpillar Spodoptera frugiperda. Of the 5-HT analogues tested for agonist action, 2-methyl-5-HT (0.1-10 μM) was a full agonist with reduced potency while α-methyl-5-HT (0.1-100 μM), 5-carboxamidotryptamine (0.1-100 μM), 5-methoxytryptamine (5-MeOT) (10 nM-10 μM), and tryptamine (1-100 μM) were partial agonists. Incubation of isolated guts with proven mammalian 5-HT receptor antagonists showed that cyproheptadine (10 nM-1 μM), MDL 72222 (1-10 μM), tropisetron (1-10 μM) and 5-benzoyloxygramine (1-10 μM) were potent non-competitive antagonists of 5-HT-induced tissue contraction. In comparison, ketanserin (0.1-1 μM) was a competitive antagonist. The mammalian selective serotonin reuptake inhibitors, clomipramine (10 nM-10 μM) and fluoxetine (10 nM-10 μM) also caused non-competitive inhibition of 5-HT-induced contraction while fluvoxamine (10 nM-10 μM) was a weak competitive antagonist. Low doses of clomipramine (0.1 μM) caused potentiation of 5-HT-induced gut contraction thereby suggesting the presence of 5-HT reuptake systems in this tissue. The contractile effects of 5-HT were inhibited by verapamil, Li⁺ and H7 and potentiated by theophylline thereby indicating that L-type Ca²⁺ channels, phosphatidylinositol second messengers and cAMP, respectively, are involved in 5-HT-induced tissue contraction. The 5-HT receptors mediating contractility in the gut of S. frugiperda have properties in common with mammalian 5-HT₂ and Drosophila 5-HT_dro2A/2B receptors. In addition, these data suggest that the tissue also contains receptors that are similar to mammalian 5-ht₆ and 5-HT₇ as well as Drosophila_dro1 receptors. However, the primary amino acid sequence of these lepidopteran 5-HT receptors will have to be elucidated before full comparisons can be made.