Binding of acetylcholine and related compounds to purified acetylcholine receptor from Torpedo Californica electroplax.
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A number of compounds showing general anesthetic action in the rotifer Brachionus calyciflorus were investigated in the presence of acetylcholine. Non-ionizing anesthetics, including tricaine, showed no interaction with acetylcholine. However, highly ionized compounds like the local anesthetics procaine and lidocaine, the muscarinic blocker and local anesthetic atropine, and the beta-adrenergic blocker propranolol showed a synergistic effect with acetylcholine. ACh increased the general anesthetic effect of these compounds in a statistically highly significant dose-dependent fashion. To account for the mechanism of this unusual and novel effect it is proposed that these compounds interact with the anesthetic binding site of the rotifer cholinoceptor ionophore in the open state. It is also proposed that non-ionizing compounds have a general membrane effect only. In addition to anesthesia, atropine and propranolol cause foot paralysis in B. calyciflorus. This other novel effect is also enhanced by acetylcholine as well as decamethonium, a neuromuscular blocker.
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The potentials of XAD-columns for the isolation of quaternary ammonium compounds from aqueous media have been investigated. When adequate amounts of counter ions (perchlorate, chloride, phosphate, nitrate) were added to the aqueous sample, to the column pretreatment fluid and to the aqueous washing fluid, most quaternary compounds investigated were retained on the column and could be recovered by elution with methanol. This approach proved also suitable for urine. Quantitation of quaternaries isolated in this way from urine samples could be performed on silicagel thin layer plates through visualization with iodine, followed by densitometric evaluation. For decamethonium detection limits were 0.1 micrograms/ml. Recoveries at the 1 micrograms/ml level were between 80--90% with variation coefficients of less than 10%.
Mechanisms of interaction between the antimicrobial drugs decamethoxinum and aethonium, which are based on bisquaternary ammonium compounds, and a phospholipid component of biological membranes, dipalmitoylphosphatidylcholine, were studied by means of liquid secondary ion mass spectrometry (LSIMS) and differential scanning calorimetry (DSC). Supramolecular complexes of the drugs with this phospholipid were recorded under secondary ion mass spectrometric conditions. The dependence of the structures of these complexes on structural parameters of the dications of the bisquaternary ammonium compounds was demonstrated. Tandem mass spectrometric investigations of the metastable decay of doubly charged ions of decamethoxinum and aethonium complexes with dipalmitoylphosphatidylcholine allowed estimation of structural parameters of these complexes in the gas phase. Interactions of decamethoxinum and aethonium with model membrane assemblies built from hydrated dipalmitoylphosphatidylcholine were studied using DSC. It was shown that while both drugs can interact with model membranes, the mechanisms of such interactions for decamethoxinum and aethonium differ. The correlation between the nature of these interactions and structural and electronic parameters of the dications of the two bisquaternary agents is discussed. Interpretation of combined mass spectrometric and calorimetric experimental data led to proposals that the molecular mechanisms of antimicrobial action of bisquaternary ammonium compounds are related to their effect on the membrane phospholipid components of microbial cells.
I. I. Mechnikov Kharkov Research Institute of Microbiology, Vaccines and Sera, Ministry of Public Health of the Ukrainian SSR. The results of mass spectrometric investigation of decamethoxine++, an antimicrobial chemotherapeutic drug, are presented. It was shown that desorption-field mass spectrometry provided recording decamethoxine++ intensive quasimolecular ions [M.Cl]+ and [M]++ forming under conditions of high electric intensity only from the intact parent molecule. Hence, the presence of the peaks in the desorption field mass spectra made it possible to definitively determine decamethoxine++ in the samples. Therefore, the procedure of desorption-field mass spectrometry proved reliable in identification of bisquaternary ammonium compounds. Ways for thermal decomposition and mass spectrometric fragmentation of the decamethoxine++ molecule under various ionization conditions are also discussed.
alpha-Synuclein is the major constituent of Lewy bodies, a pathological signature of Parkinson disease, found in the degenerating dopaminergic neurons of the substantia nigra pars compacta. Amyloidosis generating the insoluble fibrillar protein deposition has been considered to be responsible for the cell death observed in the neurodegenerative disorder. In order to develop a controlling strategy toward the amyloid formation, 1,1'-(1,10-decanediyl)-bis-[4-a-mino-2-methylquinolinium] (dequalinium), was selected and examined in terms of its specific molecular interaction with alpha-synuclein. The protein was self-oligomerized by dequalinium, which gave rise to the ladder formation on N-[2-hydroxy-1,1-bis(hydroxymethyl)ethyl]glycine/SDS-PAGE in the presence of a coupling reagent of N-(ethoxycarbonyl)-2-ethoxy-1,2-dihydroquinoline. The double-headed structure of dequalinium with the two cationic 4-aminoquinaldinium rings was demonstrated to be critical for the protein self-oligomerization. The dequalinium-binding site was located on the acidic C-terminal region of the protein with an approximate dissociation constant of 5.5 mum. The protein self-oligomerization induced by the compound has resulted in the protofibril formation of alpha-synuclein before it has developed into amyloids. The protofibrils were demonstrated to affect the membrane intactness of liposomes, and they have also been shown to influence cell viability of human neuroblastoma cells. In addition, dequalinium treatment of the alpha-synuclein-overexpressing cells exerted a significant cell death. Therefore, it is pertinent to consider that dequalinium could be used as a molecular probe to assess toxic mechanisms related to the amyloid formation of alpha-synuclein. Ultimately, the compound could be employed to develop therapeutic and preventive strategies toward alpha-synucleinopathies including Parkinson disease.
It has been shown in experiments that intramuscular injection of guaternary ammonium compounds (decamethoxine and decamine) and levorin changed the content of cholesterol, phospholipids and triglycerides in the liver of white rats. Decamethoxine decreased the content of phospholipids and cholesterol and raised the concentration of triglycerides. Decamine decreased the level of phospholipids and raised the content of cholesterol and triglycerides, while levorin minimized the content of phospholipids, cholesterol and triglycerides.
Channel blockers are compounds that disrupt the flow of current through ionic channels in membranes. We use the patch clamp technique to characterize the interactions of blocking particles with individual lens membrane channels. The mean current amplitude at many voltages is determined. The ratios of blocked to unblocked currents at several blocker concentrations are compared to a one binding site model to determine the kd and electrical distance of the site. When channel flickers are too fast to be resolved, the calculation of the power spectral density of the open channel current is useful. It is suggested that channel blockers might be useful therapeutically in some types of cataracts.
1. The mode of action of various antagonists of acetylcholine (ACh) excitatory effects on Aplysia neurones was studied under voltage clamp. ACh was applied by iontophoresis whereas antagonists were applied in the bath. Tubocurarine and hexamethonium were the most thoroughly studied compounds. 2. The 'elementary current', calculated as the ratio of the variance of the ACh noise to the mean ACh induced current, was not modified by any of the antagonists tested. 3. The evolution of the ACh induced current after a voltage jump, which is normally described by a single exponential, was modified by all the antagonists tested. A common feature of the modified relaxations was the appearance, over a certain concentration range of the antagonist, of two successive and opposite exponential components. 4. The characteristics of the composite relaxations depend on the antagonist. For a given antagonist they vary with membrane potential, ACh concentration, and antagonist concentration. 5. The noise power spectra of the ACh induced current showed changes consistent with those of the relaxations. 6. In the absence of antagonists, the current induced by a steady application of ACh increases linearly with hyperpolarization. In the presence of antagonists, the I-V curve shows a marked curvature, indicating a proportionally larger reduction of the ACh response at more negative membrane potentials. 7. The voltage sensitivity of the blocking action of hexamethonium and decamethonium is noticeably stronger than that of monovalent antagonists. 8. A model is proposed which accounts for the observed effects. It assumes that the antagonists studied bind perferentially to the 'activated' ACh-receptor complex, and convert it to a non-conducting state. Kinetic constants can be calculated for this reaction; e.g. for curare, at 12 degrees C and -80 mV, the dissociation and association constants were estimated at 0.1 sec-1 and 4 X 10(5) M-1 sec-1. 9. Partial replacement of the extracellular Na by Tris modifies the relaxations observed in the presence of hexamethonium. Hexamethonium appears less effective in the presence of Tris, which supports the hypothesis that the binding site of the antagonists is linked to the ionic channel.
Decamethoxin is shown to be able to increase membrane permeability of Pseudomonas aeruginosa, Escherichia coli and Micrococcus lysodeikticus, that is confirmed by a loss of compounds with the absorption maximum at 260 nm by cells. Parallel with this the number of viable individuals has fallen and activity of dehydrogenases has been inhibited. The aspartate and alanine aminotransferase activity was not inhibited by decamethoxin and even increased. Decamethoxin lysed the protoplasts of the tested microorganisms. At high decamethoxin concentrations (over 500 micrograms/ml for P. aeruginosa and over 200 mu/ml--for E. coli) the outflow of components from the cells of gram-negative bacteria ceased, that may be associated with the coagulation changes in the cytoplasm. A loss of the low-molecular components by M. lysodeikticus cells and lysis of protoplasts proceeded less intensely than the same processes in the gram-negative microorganisms, that is explained by a less resistance of M. lysodeikticus to decamethoxin and earlier coagulation of the cytoplasm preventing lysis.
This report documents slow changes in cochlear responses produced by electrical stimulation of the olivocochlear bundle (OCB), which provides efferent innervation to the hair cells of the cochlea. These slow changes have time constants of 25-50 sec, three orders of magnitude slower than those reported previously. Such "slow effects" are similar to classically described "fast effects" in that (1) they comprise a suppression of the compound action potential (CAP) of the auditory nerve mirrored by an enhancement of the cochlear microphonic potential (CM) generated largely by the outer hair cells; (2) the magnitude of suppression decreases as the intensity of the acoustic stimulus increases; (3) they share the same dependence on OCB stimulation rate; (4) both are extinguished upon cutting the OCB; and (5) both are blocked with similar concentrations of a variety of cholinergic antagonists as well as with strychnine and bicuculline. These observations suggest that both fast and slow effects are mediated by the same receptor and are produced by conductance changes in outer hair cells. Slow effects differ from fast effects in that (1) fast effects are greatest for acoustic stimulus frequencies between 6 and 10 kHz, whereas slow effects peak for frequencies from 12 to 16 kHz, and (2) fast effects persist over long periods of OCB stimulation, whereas slow effects diminish after 60 sec of stimulation. The time course of the slow effects can be described mathematically by assuming that each shock-burst produces, in addition to a fast effect, a small decrease in CAP amplitude that decays exponentially with a time constant that is long relative to the intershock interval. The long time constant of the slow effect compared to the fast effect suggests that it may arise from a distinct intracellular mechanism, possibly mediated by second-messenger systems.
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A method for inducing paralysis in embryonic chicks is described. This involves single injections of the neuromuscular blocking agents, D-tubocurrarine Chloride or decamethonium iodide, into 10-day embryos. The dose which optimises survival and paralysis is determined along with the effect of the drugs on embryonic growth. Decamethonium iodide at a dose of 1 mg per embryo gave maximum survival and paralysis to 18 days of incubation. Paralysis was assessed by observation of treated embryos in ovo and by examination of embryos removed from their shells between 11 and 18 days of incubation. Embryos were completely paralysed 24 hours post-injection and remained paralysed until 18 days of incubation. Paralysed embryos failed to hatch. Development of the leg musculature was severely retarded in paralysed embryos. This method of inducing paralysis has considerable advantages over previous continuous infusion methods. The growth and collagen content of the tibia in the paralysed embryos was reduced and these results, and other applications of the method, are discussed.
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