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Potassium channel blocker activates extracellular signal-regulated kinases through Pyk2 and epidermal growth factor receptor in rat cardiomyocytes.

OBJECTIVES: We sought to determine whether potassium (K(+)) channel blockers (KBs) can activate extracellular signal-regulated kinase (ERK) and to characterize the upstream signals leading to ERK activation in cardiomyocytes. BACKGROUND: Because KBs attenuate K(+) outward current, they may possibly prolong the duration of action potentials, leading to an increase in calcium (Ca(2+)) transient ([Ca(2+)](i)) in cardiomyocytes. Elevation of intracellular Ca(2+) levels can trigger various signaling events. Influx of Ca(2+) through L-type Ca(2+) channels after membrane depolarization induced activation of MEK and ERK through activation of Ras in neurons. Although KBs are frequently used to treat cardiac arrhythmias, their effect on signaling pathways remains unknown. METHODS: Primary cultured rat cardiomyocytes were stimulated with four different KBs-4-aminopyridine (4-AP), E-4031, tetra-ethylammonium and quinidine-and phosphorylation of ERK, proline-rich tyrosine kinase 2 (Pyk2) and epidermal growth factor receptor (EGFR) was detected. Action potentials were recorded by use of a conventional microelectrode. (Ca(2+))(i) was monitored by the fluorescent calcium indicator Fluo-4. RESULTS: E-4031, 4-AP, tetra-ethylammonium and quinidine induced phosphorylation of ERK. 4-Aminopyridine prolonged the duration of action potentials by 37% and increased (Ca(2+))(i) by 52% at 1 mmol/l. Pre-incubation of ethyleneglycoltetraacetic acid, 1,2-bis(2-aminophenoxy)-ethane-N,N,N',N'-tetraacetic acid tetrakis and diltiazem completely blocked this phosphorylation, whereas flufenamic acid and benzamil did not. 4-Aminopyridine induced tyrosine phosphorylation of Pyk2 and EGFR, which peaked at 5 and 10 min, respectively. Cytochalasin D, AG1478 and dominant-negative EGFR strongly inhibited the phosphorylation of ERK, whereas calphostin C, calmidazolium and KN62 did not. CONCLUSIONS: These findings indicate that KBs induce ERK activation, which starts with Ca(2+) entry through the L-type Ca(2+) channel in cardiomyocytes, and that EGFR and Pyk2 are involved in this activation.

4-Aminopyridine↗

Flufenamic and tolfenamic acids and lemakalim relax guinea-pig isolated trachea by different mechanisms.

The effects of K+ channel inhibitors on the relaxations induced by flufenamic and tolfenamic acids and lemakalim were examined in guinea-pig isolated trachea precontracted with prostaglandin F2alpha (PGF2alpha, 1 microM). Flufenamic and tolfenamic acids (0.1-33 microM) and lemakalim (0.01-33 microM) relaxed guinea-pig trachea in a concentration-dependent manner. Tetraethylammonium (0.5-2 mM), a nonspecific inhibitor of K+ channels, inhibited the relaxations induced by flufenamic and tolfenamic acids without affecting lemakalim-induced relaxation. Charybdotoxin (ChTX, 33-100 nM), an inhibitor of the large Ca2+-activated K+ channels (BK(Ca)), also inhibited the relaxations induced by flufenamic and tolfenamic acids without affecting lemakalim-induced relaxation. Glipizide (3.3-33 microM), an inhibitor of the ATP-sensitive K+ channels (K(ATP)) inhibited lemakalim-induced relaxation without affecting those induced by flufenamic and tolfenamic acids. Our results indicate that the relaxations of guinea-pig isolated trachea by flufenamic and tolfenamic acids are due to activation of BK(Ca). The relaxant mechanism of flufenamic and tolfenamic acids thus differs from that of lemakalim, an activator of K(ATP).

Animals↗

Characterization of a proton-activated, outwardly rectifying anion channel.

Anion channels are present in every mammalian cell and serve many different functions, including cell volume regulation, ion transport across epithelia, regulation of membrane potential and vesicular acidification. Here we characterize a proton-activated, outwardly rectifying current endogenously expressed in HEK293 cells. Binding of three to four protons activated the anion permeable channels at external pH below 5.5 (50% activation at pH 5.1). The proton-activated current is strongly outwardly rectifying, due to an outwardly rectifying single channel conductance and an additional voltage dependent facilitation at depolarized membrane potentials. The anion channel blocker 4,4'-diisothiocyanostilbene-2,2'-disulphonic acid (DIDS) rapidly and potently inhibited the channel (IC50: 2.9 microm). Flufenamic acid blocked this channel only slowly, while mibefradil and amiloride at high concentrations had no effect. As determined from reversal potential measurements under bi-ionic conditions, the relative permeability sequence of this channel was SCN-> I-> NO3-> Br-> Cl-. None of the previously characterized anion channel matches the properties of the proton-activated, outwardly rectifying channel. Specifically, the proton-activated and the volume-regulated anion channels are two distinct and separable populations of ion channels, each having its own set of biophysical and pharmacological properties. We also demonstrate endogenous proton-activated currents in primary cultured hippocampal astrocytes. The proton-activated current in astrocytes is also carried by anions, strongly outwardly rectifying, voltage dependent and inhibited by DIDS. Proton-activated, outwardly rectifying anion channels therefore may be a broadly expressed part of the anionic channel repertoire of mammalian cells.

4,4'-Diisothiocyanostilbene-2,2'-Disulfonic Acid↗

Drug and fatty acid effects on serum thyroid hormone binding.

We directly compared the competitor potency for serum T4 binding of 11 nonsteroidal antiinflammatory drugs; the diuretics furosemide, ethacrynic acid, and bumetanide; diphenylhydantoin; the cholecystographic contrast agents iopanoate and ipodate; and six long-chain nonesterified fatty acids (NEFA) using equilibrium dialysis. To avoid artefacts that occur in competitor studies with diluted serum or isolated binding proteins, we used undiluted normal serum, with drugs added at concentrations that achieved high therapeutic total and free serum levels at equilibrium. Drug addition was based on the measured free fraction of each drug in serum. The free T4 fraction in normal serum (Tris buffer, pH 7.4; 37 C) was between 1.40 X 10(-4) and 1.53 X 10(-4). Drug-induced increases in T4 free fraction were: fenclofenac, 90%; aspirin, 62%; meclofenamic acid, 39%; diflunisal, 37%; mefenamic acid, 31%; and furosemide, 31%. Significant increases of 7-15% occurred with diclofenac, flufenamic acid, phenylbutazone, and diphenylhydantoin. Indomethacin, ketoprofen, tolmetin, ethacrynic acid, bumetanide, iopanoate, and ipodate were inactive at the concentrations studied. Addition of 2.0 mmol/L oleic acid had a negligible effect, but 3.5 mmol/L oleic acid inhibited T3 and T4 binding significantly. Other long chain NEFA (addition of 1.5 mmol/L) gave increases in free T4 fraction as follows: arachidonic acid, 26%; linolenic acid, 23%; and linoleic acid, 11%. Stearic and palmitic acids were inactive. The effect of 5 mmol/L oleic acid in serum could be reproduced by addition of 0.5 mmol/L to serum diluted 1:10, indicating that protein binding of NEFA is the major determinant that limits their competitor potency. These findings provide a basis for anticipating which potential inhibitors may cause important changes in serum thyroid hormone binding. The time course of such effects will be influenced by the pharmacokinetics of the inhibitor itself as well as the equilibrium findings described here.

Anti-Inflammatory Agents, Non-Steroidal↗

Metabolism of N-alkyl compounds during the biosynthesis of prostaglandins. N-Dealkylation during prostaglandin biosynthesis.

The microsomal fraction of ram seminal vesicles (RSV), when fortified with arachidonic acid, catalyzed the dealkylation of various N-methyl compounds. These included an analogous series of monomethyl- and dimethyl-substituted anilines as well as the drugs aminopyrine and benzphetamine. In contrast, S-alkyl and O-alkyl compounds were poor substrates for dealkylation by RSV microsomes fortified with fatty acid. RSV microsomal N-dealkylation was completely dependent on enzyme and arachidonic acid and could be inhibited by the prostaglandin synthetase inhibitors indomethacin, phenylbutazone, and flufenamic acid as well as by anaerobic conditions. Butylated hydroxyanisole also inhibited the reaction, whereas SKF-525A and metyrapone, which are inhibitors of cytochrome P-450-dependent N-dealkylation, did not. In addition to arachidonic acid, N-dealkylation was elicited by 15-hydroperoxyarachidonic acid, tert-butyl-hydroperoxide, and hydrogen peroxide; these latter reactions were not inhibited by either prostaglandin synthetase inhibitors or anaerobic conditions but did require the presence of microsomal protein. The time course of RSV N-dealkylation, which paralleled O2 consumption by this tissue (an indicator of prostaglandin biosynthesis) implied arachidonic acid-dependent irreversible self-inactivation of catalytic activity. Apparently, oxidizing agents are formed during the interaction of hydroperoxide intermediates of prostaglandin biosynthesis with prostaglandin synthetase, with the oxidizing agents then causing both substrate N-dealkylation and destruction of the enzyme. The metabolism of N-alkyl compounds during the biosynthesis of prostaglandins may provide an additional xenobiotic oxidation pathway to cytochrome P-450-dependent monooxygenases.

Animals↗

Differential connexin expression, gap junction intercellular coupling, and hemichannel formation in NT2/D1 human neural progenitors and terminally differentiated hNT neurons.

Connexin-mediated gap junctions and open hemichannels in nonjunctional membranes represent two biologically relevant mechanisms by which neural progenitors can coordinate their response to changes in the extracellular environment. NT2/D1 cells are a teratocarcinoma progenitor line that can be induced to differentiate terminally into functional hNT neurons and NT-G nonneuronal cells. Clinical transplants of hNT neurons and experimental grafts of NT2/D1 progenitors or hNT neurons have been used in cell-replacement therapy in vivo. Previous studies have shown that NT2/D1 cells express connexin 43 (Cx43) and that NT2/D1 progenitors are capable of dye transfer. To determine whether NT2/D1 progenitors and differentiated hNT cultures express other connexins, Cx26, Cx30, Cx32, Cx36, Cx37, Cx43, and Cx46.6 mRNA and protein were analyzed. NT2/D1 progenitors express Cx30, Cx36, Cx37, and Cx43. hNT/NT-G cultures express Cx36, Cx37, and de novo Cx46.6. Cx26 and Cx32 were not expressed in NT2/D1 or hNT/NT-G cells. NT2/D1 progenitors formed functional gap junctions as assessed by dye coupling as well as open hemichannels in nonjunctional membranes as assessed by dye-uptake studies. Dye coupling was inhibited by the gap junction blocker 18alpha-glycyrrhetinic acid. Hemichannel activity was inhibited by the dual-specificity chloride channel/connexin hemichannel inhibitor flufenamic acid but not by the chloride channel inhibitor 4,4'-diisothiocyanatostilbene-2,2'-disulfonic acid. Both dye coupling and dye uptake were substantially reduced following differentiation of NT2/D1 progenitors. We conclude that the pattern of connexin expression in NT2/D1 cells changes over the course of differentiation corresponding with a reduction in biochemical coupling and hemichannel activity in differentiated cells.

Antineoplastic Agents↗

Inactivation of creatine kinase during the interaction of mefenamic acid with horseradish peroxidase and hydrogen peroxide: participation by the mefenamic acid radical.

Creatine kinase (CK) was used as a marker molecule to examine the side effects of damage to tissues by mefenamic acid, an effective drug to treat rheumatic and arthritic diseases, with horseradish peroxidase and hydrogen peroxide (HRP-H(2)O(2)). Mefenamic acid inactivated CK during its interaction with HRP-H(2)O(2). Also, diphenylamine and flufenamic acid caused a loss of CK activity, indicating the imino group, not substituent groups, in the phenyl rings have a crucial role in CK inactivation. Rapid change in mefenamic acid spectra was detected, suggesting that mefenamic acid is efficiently oxidized by HRP-H(2)O(2). Peroxidases oxidize xenobiotics to free radicals by a one-electron transfer. However, direct detection of mefenamic acid radicals by electron spin resonance (ESR) was unsuccessful. Reduced glutathione and 5,5-dimethyl-1-pyrroline-1-oxide (DMPO) in the reaction mixture containing mefenamic acid with HRP-H(2)O(2) produced ESR signals consistent with a DMPO-glutathionyl radical adduct. These results suggest that inactivation of CK is probably caused through formation of mefenamic acid radicals. Sulfhydryl groups and tryptophan residues of CK were diminished by mefenamic acid with HRP-H(2)O(2). Other SH enzymes, including alcohol dehydrogenase and glyceraldehyde-3-phosphate dehydrogenase, were very sensitive to mefenamic acid with HRP-H(2)O(2). Inactivation of SH enzymes may explain some deleterious actions of mefenamic acid.

Amino Acid Substitution↗

Influence of furosemide on the detection of flunixin meglumine in horse urine samples.

The possibility of false negative results from TLC when a diuretic is administered concomitantly with flunixin was studied. Samples were subjected to solvent extraction from acidic aqueous solutions; duplicate samples were also subjected to alkaline hydrolysis at pH 12.5. The internal standard was flufenamic acid. The quantification of flunixin was performed by HPLC and the results confirmed by GC/MS. The data show that furosemide influences the urinary concentration of flunixin.

Animals↗

Activation and inhibition of kidney CLC-K chloride channels by fenamates.

CLC-K Cl(-) channels are selectively expressed in kidney and ear, where they are pivotal for salt homeostasis, and loss-of-function mutations of CLC-Kb produce Bartter's syndrome type III. The only ligand known for CLC-K channels is a derivative of the 2-p-chlorophenoxypropionic acid (CPP), 3-phenyl-CPP, which blocks CLC-Ka, but not CLC-Kb. Here we show that in addition to this blocking site, CLC-K channels bear an activating binding site that controls channel opening. Using the voltage-clamp technique on channels expressed in Xenopus laevis oocytes, we found that niflumic acid (NFA) increases CLC-Ka and CLC-Kb currents in the 10 to 1000 microM range. Flufenamic acid (FFA) derivatives or high doses of NFA produced instead an inhibitory effect on CLC-Ka, but not on CLC-Kb, and on blocker-insensitive CLC-Ka mutants, indicating that the activating binding site is distinct from the blocker site. Evaluation of the sensitivity of CLC-Ka to derivatives of NFA and FFA together with a modeling study of these ligands allow us to conclude that one major characteristic of activating compounds is the coplanarity of the two rings of the molecules, whereas block requires a noncoplanar configuration. These molecules provide a starting point for identification of diuretics or drugs useful in the treatment of Bartter's syndrome.

Animals↗

[Comparative study on the pharmacological activities of protizinic acid and various non-steroidal anti-inflammatory agents (author's transl)].

The potency of anti-inflammatory and ulcerogenic activities of a new anti-inflammatory agent, (10-methyl-7-methoxy-2-phenothiazinyl)-2-propionic acid (protizinic acid, PRT), was compared with those of various known non-steroidal anti-inflammatory agents in 5 experimental models. The ED30 of PRT in carrageenin edema with oral administration was 18.0 mg/kg and its potency was third following indomethacin (IM) and diclofenac sodium (DF), among the 15 agents tested. The ED50 of PRT in ultraviolet erythema with oral administration and the IC50 in protein denaturation were 1.07 mg/kg and 0.89 X 10(-5)M, respectively and the activities were the most potent among all agents. The IC50 of PRT in platelet aggregation induced by arachidonic acid was 5.55 X 10(-5)M and the rank of potency was sixth following to IM, DF, flufenamic acid, aluminium and ranked fifth following azapropazone, MF, alclofenac, metiazinic acid (MA), except for basic agents, mepirizole, benzydamine hydrochloride and tiaramide hydrochloride. Thus, PRT seemed to have a relatively weak ulcerogenic activity in contrast to potent anti-inflammatory activity. Also, PRT was superior to MA, an analogue of PRT, in potency of anti-inflammatory activity, in all experimental models.

Animals↗

Possible involvement of non-steroidal anti-inflammatory drugs in vagal-mediated gastric acid secretion in rats.

Effects of several non-steroidal anti-inflammatory drugs (NSAIDs) such as aspirin (ASA), indomethacin (IM), flurbiprofen (FP), ibuprofen (IP), phenylbutazone (PBZ) and flufenamic acid (FA) were studied on the gastric ulceration and gastric acid secretion induced by restraint and water-immersion stress (RWIS) or various secretagogues in rats. These drugs significantly increased ulcer formation. IM (1, 3 and 10 mg/kg, s.c.) reduced gastric mucosal prostaglandin (PG) content dose-dependently. There was an appreciable correlation between this decrease in the PG content of gastric tissue and associated ulceration. The gastric acid secretion induced by the peripheral secretagogues, methacholine, gastrin and histamine, was not significantly influenced by IM pretreatment. In contrast, the gastric acid secretion induced by the vagal mediated secretagogues, insulin, 2-deoxy-D-glucose (2-D-G) and RWIS, was markedly increased by IM pretreatment. These effects were not observed in vagotomized rats. By intracerebroventricular (i.c.v.) injection of IM, no influence was observed on the gastric acid secretion and ulcer formation induced by 2-D-G or RWIS. These results suggest that acidic NSAIDs potentiate the gastric acid output induced by stimulation of vagus nerve activity, and prostaglandins (PGs) may influence gastric acid output by regulating vagus nerve activity.

Animals↗

Nonsteroidal anti-inflammatory drugs alter chloride and fluid transport in bovine retinal pigment epithelium.

Nonsteroidal anti-inflammatory drugs (NSAIDs) were added to the solutions bathing the apical membrane of bovine retinal pigment epithelium (RPE)-choroid explants. For example, niflumic acid (100 microM) depolarized the basolateral membrane voltage (VB) by approximately 12 mV, increased transepithelial potential by 4.5 mV, decreased intracellular Cl activity by 13 mM, decreased transepithelial resistance by 17 omega.cm2, and increased the ratio of apical to basolateral membrane resistance nearly threefold. All of these changes are consistent with an increase in basolateral membrane Cl conductance. In addition, niflumic acid caused intracellular Ca concentration to decrease by 16 nM and fluid transport rate to increase by 1.5 microliters.cm-2.h-1. Flufenamic acid, which is structurally very similar to niflumic acid, had the opposite effects on membrane voltage and resistance. Basal application of the Cl channel blocker 4,4'-diisothiocyanostilbene-2,2'-disulfonic acid or current clamping VB to the reversal potential for Cl practically abolished the niflumic acid response. The niflumic acid results suggest that certain NSAIDs can directly alter Cl conductance in the bovine RPE, apparently independently of cyclooxygenase inhibition.

Animals↗

[Prophylactic and therapeutic application of anti-inflammatory agents on the test method of carrageenin paw edema in the rat (author's transl)].

A number of anti-inflammatory substances and cyclophosphamide were tested for their anti-inflammatory activity on a modified carrageenin-tragacanth-induced oedema of the rat paw. The oral application of the substances occurred before or simultaneously with the induction of the inflammation (prophylactic) as well as 2, 6 and 24 h post-irritation (therapeutic). The paw volume was measured plethysmometrically after application of the substances at 3 and 5 h, respectively (short-term test) and 24 and 25 h, respectively (long-term test). Acetylsalicylic acid and phenylbutazone showed a good anti-inflammatory activity specially in the short-term test when given prophylactically. In contrast, flufenamic acid and indomethacin up to 6 h post-application showed both prophylactic and therapeutic activity in both short- and long-term test. The steroidal compound prednisolone was effective when used therapeutically in short-term test up to 24 h post-application as well as in long-term test up to 6 h post-application. Azapropazone and cyclophosphamide were ineffective, among other factors, because of too low a dosage.

Animals↗

Effect of inhibitor time-dependency on selectivity towards cyclooxygenase isoforms.

Cyclooxygenase (Cox) is a key enzyme in the biosynthesis of prostaglandins and, as such, is the target of non-steroidal anti-inflammatory drugs (NSAIDs). Two isoforms exist, being expressed constitutively (Cox-1), or inducibly in response to inflammatory mediators (Cox-2). Currently available NSAIDs inhibit both isoforms somewhat equipotently but selective Cox-2 inhibition may eliminate unwanted side effects. We have characterized the kinetic mechanisms of the interactions of purified recombinant human cyclooxygenase-1 and -2 (hCox-1, hCox-2) with the selective Cox-2 inhibitor N-(2-cyclohexyloxy-4-nitrophenyl)methanesulphonamide (NS-398) and some classical non-selective NSAIDs. NS-398, flurbiprofen, meclofenamic acid and indomethacin are time-dependent, irreversible inhibitors of hCox-2. The inhibition is consistent with a two-step process, involving an initial rapid equilibrium binding of enzyme and inhibitor, characterized by Ki, followed by the slow formation of a tightly bound enzyme-inhibitor complex, characterized by a first-order rate constant kon. NS-398 is a time-independent inhibitor of hCox-1, consistent with the formation of a reversible enzyme-inhibitor complex. Flurbiprofen, meclofenamic acid and indomethacin are also time-dependent inhibitors of hCox-1 and hence show little selectivity for one isoform over the other. Flufenamic acid is time independent towards both isoforms and is also non-selective. The high degree of selectivity of NS-398 towards Cox-2 results therefore from the difference in the nature of the time-dependency of inhibition of the two isoforms.

Cyclooxygenase Inhibitors↗

Fenamates and diltiazem modulate lipid-sensitive mechano-gated 2P domain K(+) channels.

A swelling-activated, background K(+) current in the corneal epithelium is characteristically activated by fenamates and inhibited by diltiazem. Fatty acids also stimulate this current, indicating that its origin is a lipid-sensitive mechano-gated 2P domain K(+) channel. In the present study, modulation of TREK-1, TREK-2, and TRAAK channels by fenamates and diltiazem was examined. TREK-1, TREK-2, and TRAAK currents transiently expressed in COS-7 cells were recorded by the perforated-patch configuration. As previously reported, arachidonic acid (20 microM) stimulated all of these channels, and a volatile anesthetic, halothane (1 mM) augmented TREK-1 and TREK-2 but not TRAAK. Flufenamic acid (FA, 100 microM), niflumic acid (NA, 100 microM), and mefenamic acid (MA, 100 microM) markedly stimulated TREK-1, TREK-2, and TRAAK. The potency sequence for the activation of TREK-1 and TREK-2 was FA > NA = MA, and the potency sequence for the activation of TRAAK was FA = NA > MA. Diltiazem (1 mM) inhibited TREK-1 and TREK-2, but not TRAAK. In conclusion, fenamates are openers of the lipid-sensitive mechano-gated 2P domain K(+) channels, and diltiazem may be a specific blocker for TREK. These novel findings could help to further understand channel functions of the mechano-gated 2P domain K(+) channels.

Animals↗

[The effect of so-called basic therapeutics and symptomatically effective antirheumatic drugs on the enzymes of DNA synthesis and DNA repair].

Investigation of DNA-synthesis and DNA-repair are important for evaluating mutagenic effects of drugs. Among the tested non steroidal antirheumatic drugs metiacinic acid, ketoprofene, and azapropazone do not show any effect on these mechanisms. Tolmetin and indometacine, however, inhibit DNA-synthesis only, whereas naproxene, oxyphenylbutazone, and flufenamic acid inhibit both DNA synthesis and repair. Gold does not influence DNA synthesis or repair, D-penicillamine inhibits DNA-synthesis only. However, Chloroquine and metabolised cyclophosphamide respecitvely impair both DNA-synthesis and repair. This effect may be also caused by azathioprine in high dosage. Application of two repair- inhibitors or of one DNA-repair-inhibitor and one directly mutagenic acting drug, e.g. cyclophosphamide, should therefore be avoided.

Apazone↗

Physical and chemical changes of medicinals in mixtures with adsorbents in the solid state. III. Determination of vapor pressure of solid drugs by steam distillation.

The vapor pressures of solid drugs were determined by the steam distillation method. Experiments using a series of benzoic acid derivatives indicated that this method offered consistent and satisfactory values for vapor pressure at about 100 degrees C. The vapor pressures of two nonsteroidal antiinflammatory drugs, flufenamic acid (FFA) and mefenamic acid (MFA), were found to be 3.8 x 10(-3) and 1.8 x 10(-4) mmHg, respectively. These values explain the difference in the rate of change to the amorphous state between mixtures of each with magnesium aluminum silicate (MAS) when they were stored under reduced pressure. It was concluded that the vapor pressures of solid drugs at about 100 degrees C, as determined by steam distillation, may be suitable indices for predicting whether or not these drugs have an inherent propensity to become amorphous readily in mixtures with an adsorbent.

Benzoates↗