SEARCH · PubMed Health
Explore indexed PubMed citations for clinical trials, systematic reviews and public health research. Read source abstracts and follow each citation to its original PubMed record.
Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.
The synthesis of the sulfonium, phosphonium and arsonium analogs of the dioxolane of Fourneau is described. The muscarinic activities of these compounds were compared with regard to the role of cationic head in the interaction with the muscarinic receptor.
Contractions of frog rectus abdominus muscles induced by suxamethonium or decamethonium, and to a lesser extent by carbamylcholine, were decreased as the extracellular calcium concentration was increased. The inhibition of all three agonist responses by 1.1 mM calcium was competitive. The contractions induced by bis-onium compounds, but not carbamylcholine, were further antagonized at higher calcium concentrations (4.4 mM) in a noncompetitive manner. This latter effect of calcium may be due to antagonism of bis-onium compounds at a peripheral anionic site. Carboxyl group carbodiimide reagents inhibited muscle contractions, and this inhibition was slowly reversible. The extent of the inhibition was increased, and its recovery delayed, by prior exposure of the muscle to an agonist. The results support suggestions that receptor activation initially involves displacement of membrane calcium. The study provides further evidence that interaction of agonists iwth nicotinic receptors results in structural changes, possibly related to increased ion flow.
1. The influence of the 2 alkane-bis-onium compounds hexafluorenium (HF1) and hexamethonium (C6) on human plasma cholinesterase (ChE) was studied with respect to the type of inhibition. 2. HF1 and C6 are reversible inhibitors of ChE. The inhibitory potency of HF1 (pI50 = 6.96; Ki = 2.4 x 10(-9)) is about 40 000-fold higher than that of C6 (pI50 = 2.4; Ki = 6.7 x 10(-2)). 3. The kinetic analysis displayed a competitive (C6) and a non-competitive (hf1) mechanism of action. 4. The inhibition of ChE by C6 is induced by a binding of C6 to the anionic site of the active center thus impairing the primary formation of the enzyme-substrate complex. HF1, however, is most probably bound to anionic side receptors in the vicinity of the active center; by that a conformational change of the enzyme protein is induced impairing the acylation step of the esteratic site.
Explore the source record for details and available documents.
Explore the source record for details and available documents.
Explore the source record for details and available documents.
Photoaffinity labeling of membrane-bound nicotinic acetylcholine receptor from Torpedo marmorata electric tissue with the ion-channel blocker [3H]TPMP+ reveals various functional states of the receptor protein if labeling is performed with ms time resolution. In the resting and in the activated state most of the label is incorporated into the alpha-polypeptide chains of the receptor complex. When equilibrated with agonists and antagonists, predominantly the delta-polypeptide chain (and to a lesser extent the beta-chain) reacts with the photolabel. Reactivity of the delta-chain increases after exposure to cholinergic effectors with a half-life slower than the kinetics of receptor activation or rapid desensitization. Agonists and antagonists stimulate photolabelling of the delta-chain with different kinetics. For acetylcholine, carbamoylcholine and suberyldicholine the half-life of the reactivity increases is 400 - 500 ms; for the antagonists hexamethonium, d-tubocurarine and flaxedil it is about 10 s. The latter slow kinetics are also observed when the receptor is preequilibrated with agonists or antagonists prior to mixing with [3H]TPMP+ and starting the photoreaction. We conclude that time-resolved photoaffinity labeling can convalently mark protein structures involved in receptor functions. Of special interest is the observation that antagonists also induce a conformational change in the receptor protein.
Explore the source record for details and available documents.
The cofactor requirements of macrophage nitric oxide (NO.) synthase suggest involvement of an NADPH-dependent flavoprotein. This prompted us to test the effect of the flavoprotein inhibitors diphenyleneiodonium (DPI), di-2-thienyliodonium (DTI), and iodoniumdiphenyl (ID) on the NO. synthases of macrophages and endothelium. DPI, DTI, and ID completely inhibited NO. synthesis by mouse macrophages, their lysates, and partially purified macrophage NO. synthase. Inhibition of NO. synthase by these agents was potent (IC50's 50-150 nM), irreversible, dependent on time and temperature, and independent of enzyme catalysis. The inhibition by DPI was blocked by NADPH, NADP+, or 2'5'-ADP, but not by NADH. Likewise, FAD or FMN, but not riboflavin or adenosine 5-diphosphoribose, protected NO. synthase from inhibition by DPI. Neither NADPH nor FAD reacted with DPI. Once NO. synthase was inhibited by DPI, neither NADPH nor FAD could restore its activity. DPI also inhibited acetylcholine-induced relaxation of norepinephrine-preconstricted rabbit aortic rings (IC50 300 nM). Inhibition of acetylcholine-induced relaxation persisted for at least 2 h after DPI was washed out. In contrast, DPI had no effect on norepinephrine-induced vasoconstriction itself nor on vasorelaxation induced by the NO.-generating agent sodium nitroprusside. These results suggest that NO. synthesis in both macrophages and endothelial cells depends on an NADPH-utilizing flavoprotein. As a new class of NO. synthase inhibitors, DPI and its analogs are likely to prove useful in analyzing the physiologic and pathophysiologic roles of NO(.).
The rate of protonophore-mediated decay of pH gradient across lipid vesicular membranes was found to be enhanced by orders of magnitude by valinomycin-K+. Experiments in the presence of gramicidin have shown that the observed rate enhancement by valinomycin-K+ is not due to collapse of the diffusion potential alone. The enhancement of the rate showed hyperbolic dependence on the concentration of valinomycin. Rate enhancement was observed in the presence of the membrane permeant cation tetraphenylphosphonium (TTP+) also. Several factors which might enhance the intrinsic H+ conductivity of protonophores were analyzed. The level of partitioning of the protonophore into the membrane and the pK of membrane-bound protonophores were measured. Valinomycin-K+ did not alter both these parameters significantly. TPP+ increased the partitioning of protonophores and decreased the pK values of membrane-bound protonophores. However, these changes were too small to explain the observed rate enhancements. We suggest that valinomycin-K+ and TPP+ enhance the H+ conductivity of protonophores by increasing the permeability of the ionized form of protonophores by forming an ion pair.
Primary cultures of rat liver Kupffer cells generated large amounts of superoxide anion radical (O2-.) when subjected to reoxygenation after a hypoxic period of at least 2 h. O2-. formation reached its maximum rate of approximately 25 nmol/10(6) cells within 1 h after reoxygenation. Two to four hours after reoxygenation, the number of injured cells began to increase and after 10 h approximately 60% of the cells were dead. During the period of O2-. release no significant difference in cell viability was observed between reoxygenated and hypoxically incubated cells, indicating a distinct time lag between O2-. release and onset of cell damage. Addition of diphenyliodonium, a specific inhibitor of the neutrophilic NADPH oxidase, to the Kupffer cells just before reoxygenation diminished both O2-. formation and cell injury up to 70%. Reoxygenation injury was completely prevented when superoxide dismutase and catalase were added immediately before reoxygenation. The results indicate that Kupffer cells subjected to hypoxia-reoxygenation generate a burst of reactive oxygen species and that this kind of "activation," probably by activating the NADPH oxidase, contributes to the self-destruction of the cells.
Antitrypanosomal activity for benzyltriphenylphosphonium salts is reported for the first time. Testing was conducted using Trypanosoma rhodesiense infected mice. Of 70 phosphorus-containing compounds tested, 21 were active. Sixteen of these active chemical species were benzyltriphenylphosphonium salts. Four were nonbenzyl triphenyl compounds. The remaining active drug was a benzyldiphenylphosphonium salt.
Suspensions of phorbol myristate acetate-activated polymorphonuclear leukocytes were analyzed with a Coulter Counter STKS hematological analyzer. Phorbol myristate acetate activation induced an increase in polymorphonuclear leukocyte volume and conductivity, while scatter was unchanged. Phorbol myristate acetate-activated neutrophils in a suspension containing nitroblue tetrazolium showed increased scatter. The rise in scatter was phorbol myristate acetate dose dependent, completely inhibited by diphenylene iodonium and partially by dimethyl sulfoxide, two inhibitors of NADPH oxidase. Zymosan-activated polymorphonuclear leukocytes were notably larger with a characteristic position on discriminant function 1 display (volume versus scatter) of the analyzer. Volume and conductivity changes were seemingly inexplicable features of phorbol myristate acetate activation. The rise in scatter was produced by cytoplasmic precipitation of reduced nitroblue tetrazolium and thus by O2-generation in phorbol myristate acetate-activated neutrophils. Zymosan phagocytosis was responsible for the notable rise in polymorphonuclear leukocyte volume. The analysis of activated polymorphonuclear leukocytes by Coulter Counter STKS may provide useful information on their activation and a pragmatic approach for studying function.
The paper reports the preparation and the chromatographic separation of new deaminated analogs of S-adenosyl(5')-3-methylthiopropylamine, i.e. S-adenosyl(5')-3-methylthiopropanol and S-inosyl(5')(-3-methylthiopropanol. These compounds can be used as specific inhibitors of polyamine biosynthesis. It is also reported the characterization of new sulfonium compounds by U.V. spectrophotometry, thin layer chromatography, high voltage electrophoresis, hydrolysis to known fragments.
Explore the source record for details and available documents.
Diphenylene iodonium is an inhibitor of the enzyme NADPH-oxidase and prevents the generation of oxygen-derived free radicals in neutrophils (Cross and Jones, 1986). Here we show that diphenylene iodonium (0.25-2 microM) inhibited, according to the dose, thrombin-induced platelet-aggregation in human washed platelets and ADP-induced platelet aggregation in platelet-rich plasma. At the concentrations which inhibited platelet aggregation diphenylene iodonium did not alter platelet concentrations of cAMP or cGMP but enhanced the anti-platelet activity of iloprost, sodium nitroprusside or cultured endothelial cells. These findings highlight the importance of free radicals as platelet pro-aggregatory agents.
The conditions of inhibition of neutrophil O2-. generating oxidase by iodonium biphenyl (IBP) were studied. In a cell free system of oxidase activation consisting of neutrophil membranes and cytosol, GTP-gamma-S, Mg2+ and arachidonic acid, the inhibitory effect of IBP depended on the redox conditions of the medium. Inhibition was observed when the medium was supplemented with dithionite or NADPH. When the cell free system was incubated with IBP in the absence of reducing agents, full oxidase activity was recovered after removal of free IBP by gel filtration. Bovine neutrophil membranes, but not cytosol, contained component(s) sensitive to IBP. Upon treatment of neutrophil membranes by IBP followed by reduction, the spectrum of reduced cytochrome b558 was modified, suggesting that cytochrome b558 is a target site for IBP.
Chronic administration of diphenylene iodonium (DPI) to rats has been shown to model the characteristics of mitochondrial myopathy. Using this model the efficacy of menadione therapy has been assessed. Menadione treatment of rats injected with DPI was associated with improved weight gain and increased survival rate. This was accompanied by an improvement in muscle function as judged by analysis of isometric twitch tension of the gastrocnemius muscle (1 Hz for 20 min). The decline in phosphocreatine (PCr) levels in the gastrocnemius muscle during stimulation and delayed recovery in PCr after stimulation were similar in the menadione treated and untreated models. Menadione treatment of the DPI model resulted in a resting intramuscular pH significantly lower than control or untreated DPI rats, but a similar decline in intramuscular pH to the DPI rats during stimulation. The changes in metabolite levels were broadly similar in both the menadione treated and untreated DPI models following stimulation, although the changes, except for increased lactate concentration, were generally less marked in the menadione-treated DPI model.