Acute Inhibitory Effect Research Articles

The Effect of Alcohol on Postprandial and Fasting Triglycerides

Alcohol has a significant additive effect on the postprandial triglyceride peak when it accompanies a meal containing fat, especially saturated fat. This results from a decrease in the breakdown of chylomicrons and VLDL remnants due to an acute inhibitory effect of alcohol on lipoprotein lipase activity. Furthermore, alcohol increases the synthesis of large VLDL particles in the liver, which is the main source of triglycerides in the hypertriglyceridemia associated with chronic excessive alcohol intake. In case of chronic consumption, lipoprotein lipase activity seems to adapt itself. The effect of alcohol on adipose tissues is less clear. Sometimes, a severe hypertriglyceridemia induced by alcohol (SHIBA) can be observed, especially in patients with type 2 diabetes mellitus and/or obesity increasing the risk of pancreatitis.

Acute inhibitory effect of neuromuscular electro stimulation on muscle sympathetic activity in chronic heart failure

Acute inhibitory effect of neuromuscular electro stimulation on muscle sympathetic activity in chronic heart failure

Acute inhibitory effects of clenbuterol on force, Ca2+ transients and action potentials in rat soleus may not involve the β2‐adrenoceptor pathway

1. Clenbuterol, a β(2)-adrenoceptor agonist, can have inhibitory and myotoxic effects on slow-twitch muscles. Clenbuterol is lipophilic and may enter into the intracellular compartment, and because of this, it is likely that clenbuterol will have different effects to classical β(2)-adrenoceptor agonists such as terbutaline. The aim of the present study is to investigate clenbuterol's effect on force, intracellular [Ca(2+)] and electrophysiology, and the role of the β(2)-adrenoceptor pathway in these effects. 2. Simultaneous measurements of isometric force and [Ca(2+)](i) were made from small bundles of rat soleus muscle fibres in which several superficial fibres had been pressure-injected with the fluorescence Ca(2+) indicator Indo-1. The muscle's electrophysiological response was measured using glass intracellular microelectrodes. 3. The most robust effect of clenbuterol was a concentration- (10-50 μmol/L) and frequency-dependent (10-80 Hz) loss of force and [Ca(2+)](i) maintenance during tetanic stimulation of muscle fibres. None of these effects were reduced in the presence of the β(2)-antagonist ICI 118551. 4. In addition clenbuterol had a significant effect on muscle electrophysiology, with action potentials measured during tetanic trains being inhibited in a concentration- and frequency-dependent manner. This response was also unchanged by pre-treatment with the β(2)-antagonist ICI 118551. 5. These results indicate that some of clenbuterol's effects are mediated through a pathway other than the β(2)-adrenoceptors.

Effects of cytochromeP-450 metabolites of arachidonic acid on the epithelial sodium channel (ENaC)

Sodium reabsorption via the epithelial Na(+) channel (ENaC) in the aldosterone-sensitive distal nephron plays a central role in the regulation of body fluid volume. Previous studies have indicated that arachidonic acid (AA) and its metabolite 11,12-EET but not other regioisomers of EETs inhibit ENaC activity in the collecting duct. The goal of this study was to investigate the endogenous metabolism of AA in cultured mpkCCD(c14) principal cells and the effects of these metabolites on ENaC activity. Liquid chromatography/mass spectrometry analysis of the mpkCCD(c14) cells indicated that these cells produce prostaglandins, 8,9-EET, 11,12-EET, 14,15-EET, 5-HETE, 12/8-HETE, and 15-HETE, but not 20-HETE. Single-channel patch-clamp experiments revealed that 8,9-EET, 14,15-EET, and 11,12-EET all decrease ENaC activity. Neither 5-, 12-, nor 15-HETE had any effect on ENaC activity. Diclofenac and ibuprofen, inhibitors of cyclooxygenase, decreased transepithelial Na(+) transport in the mpkCCD(c14) cells. Inhibition of cytochrome P-450 (CYP450) with MS-PPOH activated ENaC-mediated sodium transport when cells were pretreated with AA and diclofenac. Coexpression of CYP2C8, but not CYP4A10, with ENaC in Chinese hamster ovary cells significantly decreased ENaC activity in whole-cell experiments, whereas 11,12-EET mimicked this effect. Thus both endogenously formed EETs and their exogenous application decrease ENaC activity. Downregulation of ENaC activity by overexpression of CYP2C8 was PKA dependent and was prevented by myristoylated PKI treatment. Biotinylation experiments and single-channel analysis revealed that long-term treatment with 11,12-EET and overexpression of CYP2C8 decreased the number of channels in the membrane. In contrast, the acute inhibitory effects are mediated by a decrease in the open probability of the ENaC. We conclude that 11,12-EET, 8,9-EET, and 14,15-EET are endogenously formed eicosanoids that modulate ENaC activity in the collecting duct.

Anti‐lipolytic effects of glucocorticoids

Background Individuals with elevated glucocorticoid (GC) levels tend to develop excess visceral adiposity, and adipose tissue specific GC elevations lead to increased adipose accumulation. This opposes the well known lipolytic actions of GCs. Evidence suggests that in the long term GCs increase lipolysis, however they may also have acute antilipolytic effects. Purpose We investigate these acute effects and potential mechanisms of action. Methods 3T3-L1 adipocytes were treated with doses of corticosterone (cort) (0–100μM) for 4 hours, after which cells underwent basal lipolysis. Glycerol release was measured as a marker of lipolysis, and HSL protein expression was measured as a marker of lipase activity. Results Adipocytes treated with 25, 50 and100uM cort, levels that represent those found within the tissue, had decreased glycerol release to approximately 85, 75 and 70% of control cells respectively. With the removal of cort, basal glycerol release was normalized to levels of controls. There were no changes in total HSL expression, however trends for elevated levels of pHSLSer565 with cort treatment were observed. Conclusions High levels of GCs, as would be present at the level of the adipose tissue, have an acute inhibitory effect on adipocyte lipolysis, and this effect is likely due to changes in lipase activity. This antilipolytic effect may play a role in GC related adipose accumulation.

The Effects of Intrathecal and Systemic Gabapentin on Spinal Substance P Release

Gabapentin binds at the extracellular α2δ1 subunit of voltage- sensitive calcium channels. Some voltage-sensitive calcium channels regulate substance P release from small primary afferents. We sought to determine in vivo whether spinal and systemic gabapentin at antihyperalgesic doses will attenuate substance P release. Rats prepared with chronic intrathecal (IT) catheters received IT vehicle or gabapentin 10 minutes before intraplantar formalin (5%, 50 μL) injection. For systemic studies, vehicle or gabapentin was delivered intraperitoneally (IP) 15 minutes before formalin injection. In separate groups of rats, to assess the effect of IT or IP gabapentin upon formalin-evoked substance P release, animals received similar treatment for assessment of flinching, but underwent transcardial perfusion with 4% paraformaldehyde 10 minutes after the formalin injection. Substance P release was determined by the incidence of neurokinin 1 receptor (NK1r) internalization in the ipsilateral and contralateral superficial dorsal horn in immunofluorescent stained tissues. Unilateral intraplantar formalin evoked biphasic hindpaw flinching. IT gabapentin (100 and 200 μg) and IP gabapentin (100 and 200 mg/kg) resulted in a dose-dependent reduction in phase 2, but not phase 1, flinching in comparison with vehicle-treated rats. Intraplanatar formalin resulted in NK1r internalization in the ipsilateral, but not contralateral, superficial dorsal horn. IT gabapentin (200 μg, but not 100 μg) and IP gabapentin (200 mg/kg, but not 100 mg/kg) significantly reduced ipsilateral NK1r internalization in comparison with vehicle-treated control. Importantly, internalization evoked by IT substance P was not blocked by IT gabapentin. Systemic and spinal gabapentin have an acute inhibitory effect on the release of substance P from small primary afferents and a concurrent effect upon the initiation of facilitated pain states.

Time-dependent effects of Prkce deletion on glucose homeostasis and hepatic lipid metabolism on dietary lipid oversupply in mice

We examined the time-dependent effects of deletion of the gene encoding protein kinase C epsilon (Prkce) on glucose homeostasis, insulin secretion and hepatic lipid metabolism in fat-fed mice. Prkce(-/-) and wild-type (WT) mice were fed a high-fat diet for 1 to 16 weeks and subjected to i.p. glucose tolerance tests (ipGTT) and indirect calorimetry. We also investigated gene expression and protein levels by RT-PCR, quantitative protein profiling (isobaric tag for relative and absolute quantification; iTRAQ) and immunoblotting. Lipid levels, mitochondrial oxidative capacity and lipid metabolism were assessed in liver and primary hepatocytes. While fat-fed WT mice became glucose intolerant after 1 week, Prkce(-/-) mice exhibited normal glucose and insulin levels. iTRAQ suggested differences in lipid metabolism and oxidative phosphorylation between fat-fed WT and Prkce(-/-) animals. Liver triacylglycerols were increased in fat-fed Prkce(-/-) mice, resulting from altered lipid partitioning which promoted esterification of fatty acids in hepatocytes. In WT mice, fat feeding elevated oxygen consumption in vivo and in isolated liver mitochondria, but these increases were not seen in Prkce(-/-) mice. Prkce(-/-) hepatocytes also exhibited reduced production of reactive oxygen species (ROS) in the presence of palmitate. After 16 weeks of fat feeding, however, the improved glucose tolerance in fat-fed Prkce(-/-) mice was instead associated with increased insulin secretion during ipGTT, as we have previously reported. Prkce deletion ameliorates diet-induced glucose intolerance via two temporally distinct phenotypes. Protection against insulin resistance is associated with changes in hepatic lipid partitioning, which may reduce the acute inhibitory effects of fatty acid catabolism, such as ROS generation. In the longer term, enhancement of glucose-stimulated insulin secretion prevails.

Cyclosporin and tacrolimus impair insulin secretion and transcriptional regulation in INS‐1E beta‐cells

Introducing the calcineurin inhibitors cyclosporin (CsA) and tacrolimus (Tac) has improved the outcome of organ transplants, but complications such as new onset diabetes mellitus after transplantation (NODAT) decrease survival rates. We sought, in a beta-cell culture model, to elucidate the pathogenic mechanisms behind NODAT and the relative contribution of the calcineurin inhibitors. INS-1E cells were incubated at basal and stimulatory glucose concentrations, while exposed to pharmacologically relevant doses of CsA, Tac and vehicle for 6 or 24 h. Tac inhibited basal (P < 0.05), but not glucose-stimulated insulin secretion (GSIS) after 6 h of exposure. After 24 h, both agents inhibited basal and GSIS (P < 0.05). Calcineurin phosphatase activity was decreased by both drugs during all conditions. Apoptosis was only seen with CsA treatment, which also induced a slight suppression of calcineurin and insulin mRNA, as well as increased levels of the sterol receptor element binding protein (SREBP)-1c, a transcription factor thought to suppress genes essential for beta-cell function and induce insulin resistance. Expression levels of nuclear factor of activated T-cells (NFAT)-c1, -c2, -c3 and -c4 were not decreased notably by either drug. Tac had acute inhibitory effects on basal insulin secretion, but prolonged exposure (24 h) to Tac or CsA revealed similar suppression of insulin secretion. These prolonged effects were mirrored by a total inhibition of calcineurin activity in beta-cells. CsA showed greater inhibition of beta-cell survival and transcriptional markers, essential for beta-cell function.

Functional Consequences of the Interactions among the Neural Cell Adhesion Molecule NCAM, the Receptor Tyrosine Kinase TrkB, and the Inwardly Rectifying K+ Channel KIR3.3

Cell adhesion molecules and neurotrophin receptors are crucial for the development and the function of the nervous system. Among downstream effectors of neurotrophin receptors and recognition molecules are ion channels. Here, we provide evidence that G protein-coupled inwardly rectifying K(+) channel Kir3.3 directly binds to the neural cell adhesion molecule (NCAM) and neurotrophin receptor TrkB. We identified the binding sites for NCAM and TrkB at the C-terminal intracellular domain of Kir3.3. The interaction between NCAM, TrkB, and Kir3.3 was supported by immunocytochemical co-localization of Kir3.3, NCAM, and/or TrkB at the surface of hippocampal neurons. Co-expression of TrkB and Kir3.1/3.3 in Xenopus oocytes increased the K(+) currents evoked by Kir3.1/3.3 channels. This current enhancement was reduced by the concomitant co-expression with NCAM. Both surface fluorescence measurements of microinjected oocytes and cell surface biotinylation of transfected CHO cells indicated that the cell membrane localization of Kir3.3 is regulated by TrkB and NCAM. Furthermore, the level of Kir3.3, but not of Kir3.2, at the plasma membranes was reduced in TrkB-deficient mice, supporting the notion that TrkB regulates the cell surface expression of Kir3.3. The premature expression of developmentally late appearing Kir3.1/3.3 in hippocampal neurons led to a reduction of NCAM-induced neurite outgrowth. Our observations indicate a decisive role for the neuronal K(+) channel in regulating NCAM-dependent neurite outgrowth and attribute a physiologically meaningful role to the functional interplay of Kir3.3, NCAM, and TrkB in ontogeny.

Rapid Regulation of KATP Channel Activity by 17β-Estradiol in Pancreatic β-Cells Involves the Estrogen Receptor β and the Atrial Natriuretic Peptide Receptor

The ATP-sensitive potassium (K(ATP)) channel is a key molecule involved in glucose-stimulated insulin secretion. The activity of this channel regulates beta-cell membrane potential, glucose- induced [Ca(2+)](i) signals, and insulin release. In this study, the rapid effect of physiological concentrations of 17beta-estradiol (E2) on K(ATP) channel activity was studied in intact beta-cells by use of the patch-clamp technique. When cells from wild-type (WT) mice were used, 1 nm E2 rapidly reduced K(ATP) channel activity by 60%. The action of E2 on K(ATP) channel was not modified in beta-cells from ERalpha-/- mice, yet it was significantly reduced in cells from ERbeta-/- mice. The effect of E2 was mimicked by the ERbeta agonist 2,3-bis(4-hydroxyphenyl)-propionitrile (DPN). Activation of ERbeta by DPN enhanced glucose-induced Ca(2+) signals and insulin release. Previous evidence indicated that the acute inhibitory effects of E2 on K(ATP) channel activity involve cyclic GMP and cyclic GMP-dependent protein kinase. In this study, we used beta-cells from mice with genetic ablation of the membrane guanylate cyclase A receptor for atrial natriuretic peptide (also called the atrial natriuretic peptide receptor) (GC-A KO mice) to demonstrate the involvement of this membrane receptor in the rapid E2 actions triggered in beta-cells. E2 rapidly inhibited K(ATP) channel activity and enhanced insulin release in islets from WT mice but not in islets from GC-A KO mice. In addition, DPN reduced K(ATP) channel activity in beta-cells from WT mice, but not in beta-cells from GC-A KO mice. This work unveils a new role for ERbeta as an insulinotropic molecule that may have important physiological and pharmacological implications.

Differential desensitization of Na coupled transporters with chronic parathyroid hormone (PTH) stimulation

PTH regulates renal proximal tubule apical (BBM) and basolateral membrane (BLM) transporters including Npt2a, Na+, K+ ATPase (Na‐K), sodium hydrogen exchangers 1 and 3 (NHE1, NHE3). We have shown that the acute inhibitory effect of PTH on proximal tubule Na‐K activity disappears with chronic PTH treatment, but the inhibitory effect on Npt2a activity persists. We hypothesize that chronic PTH results in desensitization of PTH actions on Na but not phosphate transport. To address this hypothesis, we compared the effect of acute and chronic PTH stimulation on expression and function of transport proteins and signaling pathways in Sprague Dawley rat kidney and in OK cells. Treatment with PTH (5 µg/kg) for 6 h decreased Na‐K activity and Na‐K, NHE1, and NHE3 expression in rat BLM, while chronic treatment with PTH (4 days) increased Na‐K‐activity and expression above control levels. BBM Npt2a expression significantly decreased with acute and chronic PTH treatment. PTH did not affect BLM or BBM PTH receptor expression, while BLM expression of NHERF1 significantly increased. Similar findings were seen in OK cells. After chronic PTH, selective stimulation of OK cell BBM with PTH did not stimulate additional PKA and PKC activity, while stimulation of BLM significantly increased PKC activity. BBM or BLM stimulation with 8‐bromo‐cAMP resulted in further PKA activation; stimulation with phorbol myristate acetate resulted in further PKC activation. We conclude that the effects of PTH on Na transport undergo desensitization at a post‐receptor level while the effects of PTH on phosphate transport do not desensitize. The role of differential NHERF1 regulation in modulating PTH receptor‐transporter signaling is unknown. Support from VAMR.

Investigation of the acute effect of leptin on the inhibition of glycogen catabolism by insulin in rat liver perfused in situ

Leptin, a cytokine secreted by adipose tissue, has been implicated in the insulin resistance associated with obesity. Here we examined the acute influence of leptin at physiological (10ng/mL) and supraphysiological (50ng/mL and 100ng/mL) concentrations on the inhibition of glycogen catabolism promoted by insulin in rat liver perfusion experiments. Perfusion of the liver with insulin (20μU/mL) decreased the activation of glucose production (p<0.05) and glycogenolysis by cAMP (3μM). However, the infusion of leptin, at concentrations similar to those found in non-obese (10ng/mL), obese (50ng/mL), and morbidly obese (100ng/mL) individuals did not influence the acute inhibitory effect of insulin (20μU/mL) on glucose production and glycogenolysis stimulated by cAMP(p>0.05).We conclude that neither physiological nor supraphysiological concentrations of leptin directly influence the inhibition of glycogen catabolism promoted by insulin in rat liver perfused in situ.

25. Minocycline has acute inhibitory effects on human motor cortex excitability

25. Minocycline has acute inhibitory effects on human motor cortex excitability

Ethanol inhibits voltage-gated sodium channels in cultured superior cervical ganglion neurons

To determine whether actions on sodium channels contribute to ethanol's depressant effects on the autonomic nervous system, the acute effects of ethanol on Na+ currents in primary cultured superior cervical ganglion were examined by whole-cell patch clamp recordings. Ethanol inhibited Na+ currents concentration dependently, and decreased action potential firing. Ethanol (100 mM) did not affect activation curve, but resulted in a left shift of the inactivation curve and prolonged the recovery from inactivation. This finding indicates that the channels in the inactivated state are more susceptible to ethanol than those in the resting state. For the first time, this study demonstrates acute inhibitory effects of ethanol on sodium channel gating in sympathetic neurons.

Ammonia Inhibition of Methanogenesis and Identification of Process Indicators during Anaerobic Digestion

In continuously stirred tank reactor experiments using pig manure codigested with solid fractions separated from pig manure (a mass mixture ratio of 40:60) with an organic loading rate of 9.4 gVS/ldigester/day at a thermophilic temperature of 51°C, we investigated acute inhibitory effects of ammonia on methanogenesis by using pulses of ammonium chloride, and assessed whether volatile fatty acids (VFAs) could be used as process indicators. Codigestion with the solid fractions seemed to result in a slight ammonia inhibition effect, though the digestion process was stable and the methanogens were adapted to a high ammonia concentration. We found a strong negative correlation (R 2 = 0.91) between total ammonia concentration and methane gas yield. However, free ammonia concentration did not reflect the acute ammonia inhibition significantly. Compared to a control reactor which was at an ammonia concentration of 4.6 gNH4–N/l, without pulsing ammonium chloride, a 50% decrease in methane gas yield in terms of loa...

Pre‐ and postsynaptic regulation of locus coeruleus neurons after chronic morphine treatment: a study of GIRK‐knockout mice

While the acute inhibitory effect of opioids on locus coeruleus (LC) neurons is mediated primarily by the activation of G protein-gated inwardly-rectifying K(+) (GIRK) channels, the 3'-5'-cyclic adenosine monophosphate (cAMP) system has been implicated in the effects of chronic morphine exposure. Presently, the impact of chronic morphine treatment on GIRK-dependent and GIRK-independent mechanisms underlying the opioid-induced inhibition of LC neurons is unclear. Here, opioid-induced postsynaptic inhibition was studied in LC neurons from wild-type and GIRK2/GIRK3(-/-) mice at baseline and following chronic morphine treatment. The postsynaptic inhibition of LC neurons caused by the opioid agonist [Met](5) enkephalin (ME) was unaffected by chronic morphine treatment in mice of either genotype. Furthermore, chronic morphine treatment had no effect on the forskolin augmentation of the ME-induced current in wild-type LC neurons and only a minor effect on the ME-induced current in LC neurons from GIRK2/GIRK3(-/-) mice. Chronic morphine treatment did, however, lead to an increased frequency of spontaneous excitatory postsynaptic currents (EPSCs) in the LC. Interestingly, while forskolin augmented the EPSC frequency similarly in untreated and morphine-treated wild-type mice, as well as untreated GIRK2/GIRK3(-/-) mice, it failed to increase the frequency of EPSCs in morphine-treated GIRK2/GIRK3(-/-) mice. Altogether, the findings suggest that chronic morphine treatment exerts little impact on ion channels and signaling pathways that mediate the postsynaptic inhibitory effects of opioids but does enhance excitatory neurotransmission in the mouse LC.

P025 Minocycline has acute inhibitory effects on human motor cortex excitability

P025 Minocycline has acute inhibitory effects on human motor cortex excitability

Acute inhibitory effect of dronedarone, a noniodinated benzofuran analogue of amiodarone, on Na+/Ca2+ exchange current in guinea pig cardiac ventricular myocytes

Using the whole-cell voltage-clamp method, we examined an acute effect of dronedarone, a noniodinated benzofuran analogue of amiodarone, on Na+/Ca2+ exchange current (INCX) in guinea pig cardiac ventricular cells. The INCX was recorded by ramp pulses with a holding potential of -60 mV using a pipette solution containing 226 nM free Ca2+ (20 mM 1,2-bis(2-aminophenoxy)ethane-N,N,N',N'-tetraacetic acid and 10 mM Ca2+) and 20 mM Na+. The external solution contained 140 mM Na+, 1 mM Ca2+, and blockers of other currents and pumps such as Cs+, nifedipine, ryanodine, and ouabain. A selective potent NCX inhibitor, KB-R7943 (100 microM), was used to completely inhibit INCX. Dronedarone inhibited INCX in a concentration-dependent manner. The IC50 values for the outward and inward INCX inhibition were about 33 and 28 microM, respectively, with the Hill coefficient of 1 for both. The inhibitory effect of dronedarone at 50 microM on INCX did not change in the presence of trypsin in the pipette solution. Therefore, dronedarone is classified as a trypsin-insensitive NCX inhibitor and distinct from amiodarone which is a trypsin sensitive. We conclude that dronedarone inhibits INCX but the potency is tenfold less than that of amiodarone. Dronedarone may modestly inhibit INCX in a therapeutic concentration range.

In vitro and in vivo evaluation of the effects of piperine on P-gp function and expression

Piperine, a major component of black pepper, is used as spice and nutrient enhancer. The purpose of the present study was to evaluate the effects of acute and prolonged piperine exposure on cellular P-gp expression and function in vitro and in vivo. Piperine at concentrations ranging from 10 to 100 µM, determined by MTT assay to be non-cytotoxic, was observed to inhibit P-gp mediated efflux transport of [ 3H]-digoxin across L-MDR1 and Caco-2 cell monolayers. The acute inhibitory effect was dependent on piperine concentration, with abolishment of [ 3H]-digoxin polarized transport attained at 50 µM of piperine. In contrast, prolonged (48 and 72 h) co-incubation of Caco-2 cell monolayers with piperine (50 and 100 µM) increased P-gp activity through an up-regulation of cellular P-gp protein and MDR1 mRNA levels. The up-regulated protein was functionally active, as demonstrated by a higher degree of [ 3H]-digoxin efflux across the cell monolayers, but the induction was readily reversed by the removal of the spice from the culture medium. Peroral administration of piperine at the dose of 112 µg/kg body weight/day to male Wistar rats for 14 consecutive days also led to increased intestinal P-gp levels. However, there was a concomitant reduction in the rodent liver P-gp although the kidney P-gp level was unaffected. Our data suggest that caution should be exercised when piperine is to be co-administered with drugs that are P-gp substrates, particularly for patients whose diet relies heavily on pepper.

Minocycline has acute inhibitory effects on human motor cortex excitability

Minocycline has acute inhibitory effects on human motor cortex excitability