Action of the nonsteroidal anti-inflammatory agent, flufenamic acid, on calcium movements in isolated mitochondria

The TMEM16A blockers benzbromarone and MONNA cause intracellular Ca2+-release in mouse bronchial smooth muscle cells

We investigated effects of TMEM16A blockers benzbromarone, MONNA, CaCC_inhA01 and Ani9 on isometric contractions in mouse bronchial rings and on intracellular calcium in isolated bronchial myocytes. Separate concentrations of carbachol (0.1-10 μM) were applied for 10 min periods to bronchial rings, producing concentration-dependent contractions that were well maintained throughout each application period. Benzbromarone (1 μM) markedly reduced the contractions with a more pronounced effect on their sustained component (at 10 min) compared to their initial component (at 2 min). Iberiotoxin (0.3 μM) enhanced the contractions, but they were still blocked by benzbromarone. MONNA (3 μM) and CaCC_inhA01 (10 μM) had similar effects to benzbromarone, but were less potent. In contrast, Ani9 (10 μM) had no effect on carbachol-induced contractions. Confocal imaging revealed that benzbromarone (0.3 μM), MONNA (1 μM) and CaCC_inhA01 (10 μM) increased intracellular calcium in isolated myocytes loaded with Fluo-4AM. In contrast, Ani9 (10 μM) had no effect on intracellular calcium. Benzbromarone and MONNA also increased calcium in calcium-free extracellular solution, but failed to do so when intracellular stores were discharged with caffeine (10 mM). Caffeine was unable to cause further discharge of the store when applied in the presence of benzbromarone. Ryanodine (100 μM) blocked the ability of benzbromarone (0.3 μM) to increase calcium, while tetracaine (100 μM) reversibly reduced the rise in calcium induced by benzbromarone. We conclude that benzbromarone and MONNA caused intracellular calcium release, probably by opening ryanodine receptors. Their ability to block carbachol contractions was likely due to this off-target effect.

Predicting Uncoupling Toxicity of Organic Acids Based on Their Molecular Structure Using a Biophysical Model

We present a purely mechanistic model to predict protonophoric uncoupling activity EC_w of organic acids. All required input information can be derived from their chemical structure. This makes it a convenient predictive model to gain valuable information on the toxicity of organic chemicals already at an early stage of development of new commercial chemicals (e.g., in agriculture or pharmaceutical industries). A critical component of the model is the consideration of the possible formation of heterodimers from the neutral and anionic monomer, and its permeation through the membrane. The model was tested against literature data measured in chromatophores, submitochondrial particles, isolated mitochondria, and intact green algae cells with good success. It was also possible to reproduce pH-dependencies in isolated mitochondria and intact cells. Besides the prediction of the EC_w, the mechanistic nature of the model allows researchers to draw direct conclusions on the impact of single input factors such as pH- and voltage-gradients across the membrane, the anionic and neutral membrane permeability, and the heterodimerization constant. These insights are of importance in drug design or chemical regulation.

Tolfenamic Acid

Tolfenamic acid (TA) is a nonsteroidal antiinflammatory drug and belongs to the group of fenamates. It is used as a potent pain reliever in the treatment of acute migraine attacks, and disorders like dysmenorrhea, rheumatoid, and osteoarthritis. TA has shown excellent in vitro antibacterial activity against certain ATCC strains of bacteria when complexed with bismuth(III). It has also been reported to block pathological processes associated with Alzheimer's disease. In the recent past, TA has also been used as a novel anticancer agent for the treatment of various cancers. In view of the clinical importance of TA, a comprehensive review of the physical and pharmaceutical properties and details of the various analytical methods used for the assay of the drug in pharmaceutical and biological systems has been made. The methods reviewed include identification tests and titrimetric, spectrophotometric, chromatographic, electrochemical, thermal, microscopic, enzymatic, and solid-state techniques. Along with the analytical profile, the stability and degradation of TA, its pharmacology and pharmacokinetics, dosage forms and dose, adverse effects and toxicity, and interactions have been discussed.

Pharmacological comparison of novel synthetic fenamate analogues with econazole and 2-APB on the inhibition of TRPM2 channels

BACKGROUND AND PURPOSE

Fenamate analogues, econazole and 2-aminoethoxydiphenyl borate (2-APB) are inhibitors of transient receptor potential melastatin 2 (TRPM2) channels and are used as research tools. However, these compounds have different chemical structures and therapeutic applications. Here we have investigated the pharmacological profile of TRPM2 channels by application of newly synthesized fenamate analogues and the existing channel blockers.

EXPERIMENTAL APPROACH

Human TRPM2 channels in tetracycline-regulated pcDNA4/TO vectors were transfected into HEK293 T-REx cells and the expression was induced by tetracycline. Whole cell currents were recorded by patch-clamp techniques. Ca(2+) influx or release was monitored by fluorometry.

KEY RESULTS

Flufenamic acid (FFA), mefenamic acid (MFA) and niflumic acid (NFA) concentration-dependently inhibited TRPM2 current with potency order FFA > MFA = NFA. Modification of the 2-phenylamino ring by substitution of the trifluoromethyl group in FFA with -CH(3), -F, -CF(3), -OCH(3), -OCH(2)CH(3), -COOH, and -NO(2) at various positions, reduced channel blocking potency. The conservative substitution of 3-CF(3) in FFA by -CH(3) (3-MFA), however, gave the most potent fenamate analogue with an IC(50) of 76 µM, comparable to that of FFA, but unlike FFA, had no effect on Ca(2+) release. 3-MFA and FFA inhibited the channel intracellularly. Econazole and 2-APB showed non-selectivity by altering cytosolic Ca(2+) movement. Econazole also evoked a non-selective current.

CONCLUSION AND IMPLICATIONS

The fenamate analogue 3-MFA was more selective than other TRPM2 channel blockers. FFA, 2-APB and econazole should be used with caution as TRPM2 channel blockers, as these compounds can interfere with intracellular Ca(2+) movement.

Functional distinctions in cytosolic calcium regulation between cells of the glomerular filtration barrier

The importance of intracellular calcium ([Ca(2+)]i) regulation in the glomerular filtration barrier (GFB) has recently been highlighted by mutations in the cation channel TRPC6, resulting in a renal-specific phenotype. We examined the effects of FFA, a tool that can activate TRPC6, on [Ca(2+)]i in human conditionally immortalised glomerular endothelial cells (ciGEnC) and human podocytes (ciPod) that form the GFB. Changes in [Ca(2+)]i stimulated by FFA were measured in Fura 2-AM loaded cells. In GEnC, cell activation by FFA was dependent on external Ca(2+), yet in ciPod it was not. Depletion of internal Ca(2+) stores with thapsigargin did not affect cell activation by FFA in ciGEnC, but inhibited it in ciPod in a nephrin-dependent manner, demonstrated using nephrin deficient (ND) ciPod in conjunction with nephrin rescue experiments. FFA induced [Ca(2+)]i store release in ciPod, but not in ciGEnC or ND ciPod. In parallel, there were differences in the localisation of overexpressed TRPC6 between ciGEnC and ciPod. Furthermore, co-transfection of nephrin with TRPC6 in HEK293 cells reduced the FFA-induced increase in [Ca(2+)]i and nephrin clustering altered TRPC6 distribution. In conclusion, cell activation by FFA in podocytes stimulates the opening of a Ca(2+) channel, probably TRPC6, in a nephrin-dependent manner with a different activation profile to GEnC.

Antimicrobial peptide-induced apoptotic death of leishmania results from calcium-de pend ent, caspase-independent mitochondrial toxicity

alpha- and -defensin-, magainin-, and cathelicidin-type antimicrobial peptides (AMPs) can kill the pathogenic protozoan Leishmania. Comparative studies of a panel of AMPs have defined two distinct groups: those that induce nonapoptotic (Class I) and apoptotic (Class II) parasite killing based on their differential ability to induce phosphatidyl serine exposure, loss of mitochondrial membrane potential and decreased ATP production, induction of caspase-3/7 and -12 activity, and DNA degradation. Class II AMPs cause rapid influx of the vital stain SYTOX and an increase in intracellular Ca2+, whereas Class I AMPs cause a slow accumulation of SYTOX and do not affect intracellular Ca2+ levels. Inhibitors of cysteine or caspase proteases diminished fast influx of SYTOX through the surface membrane and DNA degradation but do not ablate the annexin V staining or the induction of apoptosis by Class II AMPs. This suggests that the changes in surface permeability in AMP-mediated apoptosis are related to the downstream events of intracellular cysteine/caspase activation or the loss of ATP. The activation of caspase-12-like activity was Ca(2+)-dependent, and inhibitors of voltage-gated and nonspecific Ca2+ channels diminished this activity. Flufenamic acid, a nonspecific Ca2+ inhibitor, completely ablated AMP-induced mitochondrial dysfunction and cell death, indicating the importance of dysregulation of Ca2+ in antimicrobial peptide-induced apoptosis.

Flufenamic acid is a tool for investigating TRPC6-mediated calcium signalling in human conditionally immortalised podocytes and HEK293 cells

Mutations in the cation channel TRPC6 result in a renal-specific phenotype of familial nephrotic syndrome, affecting intracellular calcium ([Ca(2+)](i)) signalling in the glomerular podocyte. Tools to study native TRPC6 activity are scarce, although there has been recent success with flufenamic acid (FFA). We confirm the specificity of FFA for TRPC6 both in an artificial expression system and in a human conditionally immortalised podocyte cell line (ciPod). Cells were loaded with fura-2AM and changes in intracellular calcium ([Ca(2+)](i)) were calculated. 200microM FFA induced an increase in [Ca(2+)](i) in HEK293 cells with native TRPC6 expression, which was enhanced by overexpression of TRPC6 and completely blocked in the absence of extracellular calcium. Expressed TRPC7 did not significantly affect the response to FFA whereas expressed TRPC3 reduced it. FFA also induced an increase ciPod in [Ca(2+)](i), which was inhibited using SKF96365 and 2-APB, but not indomethacin. In ciPod, adenovirus (Ad-v) wild type (WT) TRPC6 increased [Ca(2+)](i) activity to FFA compared to native TRPC6, whereas activity was significantly reduced with Ad-v dominant negative (DN) TRPC6. The niflumic acid (NFA) induced increase in [Ca(2+)](i) in ciPod was not affected by Ad-v TRPC6 DN, and in HEK293 cells was not affected by WT TRPC6. In conclusion, FFA activates TRPC6 [Ca(2+)](i) signalling in both ciPod and HEK293 cells independently of TRPC3 and TRPC7, and independently of properties of the fenamate family.

Flufenamic acid affects multiple currents and causes intracellular Ca2+ release in Aplysia bag cell neurons

Flufenamic acid (FFA) is a nonsteroidal antiinflammatory agent, commonly used to block nonselective cation channels. We previously reported that FFA potentiated, rather than inhibited, a cation current in Aplysia bag cell neurons. Prompted by this paradoxical result, the present study examined the effects of FFA on membrane currents and intracellular Ca2+ in cultured bag cell neurons. Under whole cell voltage clamp, FFA evoked either outward (I out) or inward (I in) currents. I out had a rapid onset, was inhibited by the K+ channel blocker, tetraethylammonium, and was associated with both an increase in membrane conductance and a negative shift in the whole cell current reversal potential. I in developed more slowly, was inhibited by the cation channel blocker, Gd3+, and was concomitant with both an increased conductance and positive shift in reversal potential. FFA also enhanced the use-dependent inactivation and caused a positive-shift in the activation curve of the voltage-dependent Ca2+ current. Furthermore, as measured by ratiometric imaging, FFA produced a rise in intracellular Ca2+ that persisted in the absence of extracellular Ca2+ and was reduced by depleting either the endoplasmic reticulum and/or mitochondrial stores. Ca2+ appeared to be involved in the activation of I in, as strong intracellular Ca2+ buffering effectively eliminated I in but did not alter I out. Finally, the effects of FFA were likely not due to block of cyclooxygenase given that the general cyclooxygenase inhibitor, indomethacin, failed to evoke either current. That FFA influences a number of neuronal properties needs to be taken into consideration when employing it as a cation channel antagonist.

Intracellular Ca2+release by flufenamic acid and other blockers of the non-selective cation channel

We report in this paper using measurement of intracellular free Ca2+ with fura-2, that flufenamic acid and several related blockers of the 25 pS Ca(2+)-activated non-selective cation channel cause release of Ca2+ from an intracellular store other than the endoplasmic reticulum, possibly from mitochondria. A new compound, 4'-methyl-DPC, is found to be as effective in blocking non-selective cation channels as other flufenamate analogs but, like the parent compound, the non-selective cation channel blocker DPC, it does not cause release of Ca2+ from intracellular stores. DPC and 4'-methyl-DPC are thus the most suitable of the available blockers of non-selective cation channels for use in studies on the role of these channels in normal cell function.

Effect of pH on skin permeation enhancement of acidic drugs by l-menthol-ethanol system

The effect of pH on the skin permeation enhancement of three acidic drugs by the l-menthol-ethanol system was investigated. The total flux of acidic drugs from the system remarkably varied over the pH range 3.0-8.0, and the permeation enhancement factor depended on the system pH and drug. A skin permeation model, which consists of two permeant (unionized and ionized) species, two system (oily and aqueous) phases, and two permeation (lipid and pore) pathways, was developed. The assumptions were made that only the unionized species can distribute to the oily phase and transport via the lipid pathway. The model explained the relationship between the concentration of drug in the aqueous phase and system pH. The skin permeability data were also described by the model and permeability coefficients corresponding to the physicochemical properties of permeant were calculated for the lipid and pore pathways. The model simulation showed that the permeation of acidic drugs occurred from the aqueous phase and the oily phase acted as a reservoir. Whether the total flux increased with increase of pH was dependent on the lipophilicity of drug. These results suggest that the pH of l-menthol-ethanol system should be given attention to elicit the maximum permeation enhancement.

Flufenamic acid as an inducer of mitochondrial permeability transition

To assess the mechanism by which mitochondrial permeability transition (MPT) is induced by the nonpolar carboxylic acids, we investigated the effects of flufenamic acid (3'-trifluoromethyl diphenylamine-2-carboxylic acid, FA) on mitochondrial respiration, electrical transmembrane potential difference (delta psi), osmotic swelling, Ca2+ efflux, NAD(P)H oxidation and reactive oxygen species (ROS) generation. Succinate-energized isolated rat liver mitochondria incubated in the absence or presence of 10 microM Ca2+, 5 microM ruthenium red (RR) or 1 microM cyclosporin A (CsA) were used. The dose response-curves for both respiration release and delta psi dissipation were nearly linear, presenting an IC50 of approximately 10 microM and reaching saturation within 25-50 microM, indicating that FA causes mitochondrial uncoupling by a protonophoric mechanism. Within this same concentration range FA showed the ability to induce MPT in energized mitochondria incubated with 10 microM Ca2+, followed by delta psi dissipation and Ca2+ efflux, and even in deenergized mitochondria incubated with 0.5 mM Ca2+. ADP, Mg2+, trifluoperazine (TFP) and N-ethylmaleimide (NEM) reduced the extent of FA-promoted swelling in energized mitochondria by approximately one half, whereas dithiothreitol (DTT) slightly enhanced it. NAD(P)H oxidation and ROS generation (H2O2 production) by mitochondria were markedly stimulated by FA; these responses were partly prevented by CsA, suggesting that they may be implicated as both a cause and effect of FA-induced MPT. FA incubated with mitochondria under swelling assay conditions caused a decrease of approximately 40% in the content of protein thiol groups reacting with 5,5'-dithiobis(2-nitrobenzoic acid) (DTNB). The present results are consistent with a ROS-intermediated sensitization of MPT by a direct or indirect FA interaction with inner mitochondrial membrane at a site which is in equilibrium with the NAD(P)H pool, namely thiol groups of integral membrane proteins.

Multiple action sites of flufenamate on ion transport across the rat distal colon

The antisecretory effects of flufenamate in the rat distal colon were investigated with the Ussing-chamber and the patch-clamp method as well as by measurements of the intracellular Ca(2+) concentration using fura-2-loaded isolated crypts. Flufenamate (5.10(-4) mol l(-1)) suppressed the short-circuit current (Isc) induced by carbachol (5.10(-5) mol l(-1)), forskolin (5.10(-6) mol l(-1)) and the Isc induced by the membrane-permeable analogue of cyclic AMP, CPT - cyclic AMP (10(-4) mol l(-1)). Indomethacin (10(-6) - 10(-4) mol l(-1)) did not mimic the effect of flufenamate, indicating that the antisecretory effect of flufenamate is not related to the inhibition of the cyclo-oxygenase. When the basolateral membrane was depolarized by a high K(+) concentration and a Cl(-) current was induced by a mucosally directed Cl(-) gradient, the forskolin-stimulated Cl(-) current was blocked by flufenamate, indicating an inhibition of the cyclic AMP-stimulated apical Cl(-) conductance. When the apical membrane was permeabilized by the ionophore, nystatin, flufenamate decreased the basolateral K(+) conductance and inhibited the Na(+) - K(+)-ATPase. Patch-clamp experiments revealed a variable effect of flufenamate on membrane currents. In seven out of 11 crypt cells the drug induced an increase of the K(+) current, whereas in the remaining four cells an inhibition was observed. Experiments with fura-2-loaded isolated crypts indicated that flufenamate increased the basal as well as the carbachol-stimulated intracellular Ca(2+) concentration. These results demonstrate that flufenamate possesses multiple action sites in the rat colon: The apical Cl(-) conductance, basolateral K(+) conductances and the Na(+) - K(+)-ATPase.

Metabolic effects and distribution space of flufenamic acid in the isolated perfused rat liver

The following aspects were investigated in the present work: (a) the action of flufenamic acid on hepatic metabolism (oxygen uptake, glycolysis, gluconeogenesis, uricogenesis and glycogenolysis), (b) the action of flufenamic acid on the cellular adenine nucleotide levels, and (c) the transport and distribution space of flufenamic acid in the liver parenchyma. The experimental system was the isolated perfused rat liver. Perfusion was accomplished in an open, non-recirculating system. The perfusion fluid was Krebs/Henseleit-bicarbonate buffer (pH 7.4), saturated with a mixture of oxygen and carbon dioxide (95:5) by means of a membrane oxygenator and heated to 37 degrees C. The distribution space of flufenamic acid was measured by means of the multiple-indicator dilution technique with constant infusion (step input) of [3H]water plus flufenamic acid. The results of the present work indicate that the metabolic effects of flufenamic acid are the consequence of an uncoupling of oxidative phosphorylation, a conclusion based on the following observations: (a) flufenamic acid increased oxygen uptake, a common property of all uncouplers; (b) the drug also increased glycolysis and glycogenolysis in livers from fed rats (these are expected compensatory phenomena for the decreased mitochondrial ATP formation); (c) flufenamic acid inhibited glucose production from fructose, an energy-dependent process; (d) the cellular ATP levels were decreased by flufenamic acid whereas the AMP levels were increased; and (e) the total adenine nucleotide content was decreased by flufenamic acid and uric acid production was stimulated. Indicator-dilution experiments with flufenamic acid revealed that this substance undergoes flow-limited distribution in the liver and that its apparent distribution space greatly exceeds the aqueous space of the liver. Flufenamic acid changed its behaviour when the portal concentration was increased from 25 to 50 microM. At 25 microM the initial upslope of the outflow profile clearly preceded that of all other concentrations. From the trend of the curves obtained with 50, 100 and 250 microM, one would expect an initial upslope situated at the right of the 50-microM curve. Furthermore, the time of appearance of flufenamic acid in the outflowing perfusate was practically the same irrespective of the portal concentration. For theoretical reasons one would expect progressively longer appearance times when the portal concentration was decreased. It is possible that the amount of flufenamic acid bound to the cell membranes during the early stages of the infusion produced changes that enabled these structures to bind a larger quantity of the drug than originally possible.

Fenamates inhibit contraction of guinea-pig isolated bronchus in vitro independent of prostanoid synthesis inhibition

The inhibitory and relaxant effects of flufenamic and tolfenamic acids on guinea-pig isolated bronchus were compared with those of verapamil and indomethacin. Flufenamic and tolfenamic acids (each drug, 20 microM) and verapamil (1 microM) inhibited bronchial contraction induced by Ca2+, KCl or PGF2alpha whereas indomethacin (20 microM) had no inhibitory effect. Only verapamil, but not flufenamic and tolfenamic acids and indomethacin, inhibited methacholine-induced contraction. Flufenamic and tolfenamic acids and verapamil (each drug, 0.1-33 microM) relaxed the bronchus precontracted by KCl or PGF2alpha. In contrast, indomethacin (0.1-33 microM) did not relax KCl- or PGF2alpha-precontracted bronchus. Verapamil, but not flufenamic and tolfenamic acids and indomethacin, relaxed methacholine precontracted bronchus. In conclusion, fenamates inhibit Ca2+-, KCl- and PGF2alpha-induced contractions in guinea-pig isolated bronchus in a manner involving inhibition of Ca2+ influx but not inhibition of prostanoid synthesis.

Mechanism of action of the non-steroidal anti-inflammatory drug flufenamate on [Ca2+]i and Ca(2+)-activated currents in neurons

We have shown previously that the non-steroidal anti-inflammatory drug flufenamate (FFA) causes a maintained increase in [Ca2+]i and transient increases in a Ca(2+)-activated nonselective cation current (ICAN) and a Ca(2+)-activated slow, outward Cl- current (lo-slow) in molluscan neurons [Shaw T., Lee R.J., Partridge L.D. Action of diphenylamine carboxylate derivatives, a family of non-steroidal anti-inflammatory drugs, on [Ca2+]i and Ca(2+)-activated channels in neurons. Neurosci Lett 1995; 190:121-124]. Here we demonstrate that pretreatment of neurons with 10 microM thapsigargin eliminates the FFA-induced increase in [Ca2+]i and substantially reduces both ICAN and Io-slow supporting the hypothesis that the FFA-induced increase in [Ca2+]i results primarily from Ca2+ release from a thapsigargin-sensitive intracellular store. The [Ca2+]i response appears to be sustained, not by influx of extracellular Ca2+, but by inhibitory effects of FFA on Ca2+ removal from the cytosol. Inhibition of Ca2+ efflux may be an important component of the FFA-induced activation of both ICAN and Io-slow, as Ca2+ release by thapsigargin alone is not sufficient to activate either current. Our data also demonstrate that the effects of FFA on [Ca2+]i, ICAN and Io-slow are reversible and suggest that protein phosphorylation as well as an increase in [Ca2+]i are involved in the FFA-induced activation of Io-slow. Effects on neuronal Ca2+ handling as well as activation of ICAN or Io-slow may partially explain the analgesic effects of FFA.

Pharmacological and functional properties of voltage-independent Ca2+ channels

During the last few years, considerable progress has taken place in our knowledge of the molecular and functional properties of the various voltage-independent Ca2+ channels. In addition to the ionotropic receptor-channels (ROCs), that are not discussed in the present review, these channels include the SMOCs, activated via second messengers or other transducing processes directly triggered by receptor activation; and the SOCCs, activated as a consequence of depletion of the rapidly exchanging Ca2+ stores in the cytoplasm. In parallel, a pharmacological approach to the study of these channels has been developed, based primarily on heterogeneous drugs already known for different biological effects, and subsequently recognized as voltage-independent Ca(2+)-channel blockers. From the systematic analysis of the effects of these drugs new information has emerged about SMOCs and SOCCs function. In addition, pharmacological blockade of these channels appears to have beneficial therapeutic effects in pathological conditions such as tumoral cell growth, inflammation and immunity. At the moment the field is rapidly evolving, with major developments expected in the years ahead.

Niflumic acid-induced increase in potassium currents in frog motor nerve terminals: effects on transmitter release

The actions of the nonsteroidal antiinflammatory drug niflumic acid were studied on frog neuromuscular preparations by conventional electrophysiological techniques. Niflumic acid reduced the amplitude and increased the latency of endplate potentials in a concentration-dependent manner. Neuromuscular junctions pretreated with niflumic acid (0.05-0.5 mM) showed much less depression than control when they were stimulated with trains of impulses. Inhibition of acetylcholine release was reverted by raising the extracellular Ca(2+) concentration but not by simply washing out the preparations with niflumic acid-free solutions. Pretreatment with indomethacin (0.1 mM), another nonsteroidal antiinflammatory drug, did not affect the niflumic acid-induced inhibition of evoked responses. Niflumic acid (0.1 mM) did not change the amplitude of miniature endplate potentials and had a dual action on the frequency of miniatures: it decreased their frequency at 0.1 mM whereas it produced an enormous increase in the rate of spontaneous discharge at 0.5 mM. Niflumic acid (0.1 - 1 mM) reversibly increased the amplitude and affected the kinetics of presynaptic voltage-activated K+ current and Ca(2+)-activated K(+) current in a concentration-dependent manner. Niflumic acid (0.1 - 1 mM) irreversibly decreased the amplitude and reversibly affected the kinetics of the nodal Na(+) current. Indomethacin (0.1 mM) had no effect on presynaptic currents. In conclusion, niflumic acid reduces acetylcholine release by increasing presynaptic K+ currents. This may shorten the depolarizing phase of the presynaptic action potential and may reduce the entry of Ca(2+) with each impulse.

Action of diphenylamine carboxylate derivatives, a family of non-steroidal anti-inflammatory drugs, on [Ca2+]i and Ca(2+)-activated channels in neurons

Ca(2+)-activated channels, including Ca(2+)-activated non-selective (CAN) channels and Ca(2+)-activated Cl- channels play important roles in regulating the electrical activity of neurons. No blockers of neuronal CAN channels have been previously reported. We used 2-electrode voltage clamping to measure membrane currents and fura-2 fluorescence imaging to measure [Ca2+]i in molluscan neurons. We show that the diphenylamine carboxylate derivative flufenamate (FFA), but not mefenamate or the parent compound, cause a transient increase in ICAN and a slow outward current, and a maintained increase in [Ca2+]i. We interpret this as a FFA-dependent release of Ca2+ from intracellular stores and Ca2+ influx, [Ca2+]i-dependent activation of the CAN and slow outward currents, and slow FFA-dependent channel block.

Real-time detection of mitochondrial inhibition at frog motor nerve terminals using increases in the spatial variance in probability of transmitter release

The effects of Hg2+, methyl mercury, and flufenamic acid, all of which inhibit mitochondria, were examined at frog motor nerve terminals. Unbiased estimates of m (no. of transmitter quanta released), n (no. of functional release sites), p (probability of release), and vars p (spatial variance in p) were obtained using K(+)-induced asynchronous neurosecretion (m, n and p not having the same definitions as with nerve-evoked release). Transient but significant increases in m, n, p and vars p were found with all three agents. These findings indicate that mitochondrial inhibition and release of sequestered Ca2+ can be detected as a real-time increase in vars p. The results also suggest that changes in vars p might be used to differentiate between cellular (membrane) and subcellular (organellar) actions of drugs at the nerve terminal.

Alterations in mitochondrial function and morphology in chronic liver disease: pathogenesis and potential for therapeutic intervention

Studies assessing mitochondrial function and structure in livers from humans or experimental animals with chronic liver disease, including liver cirrhosis, revealed a variety of alterations in comparison with normal subjects or control animals. Depending on the etiology of chronic liver disease, the function of the electron transport chain and/or ATP synthesis was found to be impaired, leading to decreased oxidative metabolism of various substrates and to impaired recovery of the hepatic energy state after a metabolic insult. Changes in mitochondrial structure include megamitochondria with reduced cristae, dilatation of mitochondrial cristae and crystalloid inclusions in the mitochondrial matrix. The most important strategies to maintain an adequate mitochondrial function per liver are mitochondrial proliferation and increases in the activity of critical enzymes or in the content of cofactors per mitochondrion. Possibilities to assess hepatic mitochondrial function and to treat mitochondrial dysfunction in patients with chronic liver disease are discussed.

Inhibitors of nonselective cation channels in cells of the blood-brain barrier

In the antiluminal membrane of isolated capillaries of rat and porcine brain (blood-brain barrier) nonselective cation channels with g = 31 pS were observed in cell-excised membrane patches. The channel inactivated by decreasing cytosolic Ca2+ below 1 microM and was inhibited by 1 mM ATP on the intracellular side. Anions and divalent cations did not pass the channel, but Na+ and K+ were equally permeant. Like the nonselective cation channel of rat exocrine pancreatic cells, the channel in cerebral capillary endothelial cells was inhibited reversibly by derivatives of diphenylamine-2-carboxylate (DPC), like 3',5-dichlorodiphenylamine-2-carboxylic acid (DCDPC, ki = 1 microM), and flufenamic acid (ki = 4.9 microM). 4'-methyldiphenylamine-2-carboxylic acid (4-MDPC), 5-chloro-2(3-trifluormethylphenylamino)-3-nitrobenzoic acid, and 5-nitro-2-(3-phenylpropylamino)-2-carboxylic acid (NPPB), as well as the antiinflammatory drug ((Z)-5-chloro2,3-dihydro-3-(hydroxy-2-thienylmethylene)-2-ox o-1H-indole-1- carboxamide (Tenidap)) had a relatively low blocking potency (ki > 10 microM). Gadolinium (10 microM), a blocker of stretch-activated channels, inhibited the nonselective cation channel potently.

Flufenamic acid, mefenamic acid and niflumic acid inhibit single nonselective cation channels in the rat exocrine pancreas

The non-steroidal anti-inflammatory drugs, flufenamic acid, mefenamic acid and niflumic acid, block Ca2(+)-activated non-selective cation channels in inside-out patches from the basolateral membrane of rat exocrine pancreatic cells. Half-maximal inhibition was about 10 microM for flufenamic acid and mefenamic acid, whereas niflumic acid was less potent (IC50 about 50 microM). Indomethacin, aspirin, diltiazem and ibuprofen (100 microM) had not effect. It is concluded that the inhibitory effect of flufenamate, mefenamate and niflumate is dependent on the specific structure, consisting of two phenyl rings linked by an amino bridge.

The involvement of lactate and calcium as mediators of the electrical and mechanical responses of the myocardium to conditions of simulated ischaemia

1. Rat isolated and superfused atria were exposed to a lactate-containing solution simulating the composition of extracellular fluid during myocardial ischaemia (SI). 2. Atria subjected to SI showed a decreased adenosine 5'-triphosphate (ATP) content, a rise in diastolic tension, a diminished conduction velocity of action potentials and shortened refractory periods. All these changes were less pronounced during lactate-free SI. 3. Atria preloaded with calcium displayed exaggerated responses measured electrically and mechanically during exposure to SI, whereas atria previously depleted of calcium displayed diminished electrical and mechanical responses to SI. Neither calcium loading nor calcium depletion modified the SI-induced depletion of the atrial stores of ATP. 4. Sulphinpyrazone protected atria against all aspects of the response to SI, but failed to protect the muscle under conditions of lactate-free SI. It is concluded that during SI, sulphinpyrazone protects against a lactate-mediated inhibition of the glycolytic synthesis of ATP. 5. Flufenamate exaggerated all responses of the atria to SI. These deleterious actions were still observed during lactate-free SI. It is concluded that flufenamate inhibits the synthesis of ATP in the mitochondria.