The thiol-oxidizing agent diamide increases transmitter release by decreasing calcium requirements for neuromuscular transmission in the frog

Modification of ionic currents underlying action potentials in mouse nerve terminals by the thiol-oxidizing agent diamide

The effect of diamide, a thiol-oxidizing agent, was tested using electrophysiological techniques to determine whether its ability to alter neuromuscular transmission in vitro could be attributed to alterations of ion channels controlling neuronal excitability and/or acetylcholine release. In mouse triangularis sterni preparations, diamide transiently increased the evoked release of acetylcholine and then blocked release. Extracellular recording of perineural waveforms associated with neuronal action potentials at motor nerve terminals showed that diamide reduced the waveforms associated with the delayed rectifier K+ current, a Ca2+ current and a Ca(2+)-activated K+ current (IK,Ca). Inhibition of quantal transmitter release was not associated with failure of action potentials to invade nerve terminals. Thus, diamide modifies the ionic currents underlying the nerve terminal action potential, some of these changes probably account for the complex effects of diamide on quantal transmission.

Sensory neuropeptide-mediated bronchoconstriction of the guinea pig lung by diamide; a comparison to hydrogen peroxide

The effect of the thiol oxidizing agent diamide on airway conductance, dynamic compliance and perfusion flow of isolated perfused and ventilated guinea pig lungs was investigated. When infused in the pulmonary circulation, diamide (100 microM) induced bronchoconstriction, but no effect on perfusion flow was observed. Although diamide exposure induced the formation of thromboxane A2, the thromboxane/prostaglandin endoperoxide receptor antagonist L-670,596 did not affect the decrease in conductance and compliance induced by diamide. Diamide induced the release of the sensory neuropeptide calcitonin gene-related peptide. The bronchoconstriction and the release of calcitonin gene-related peptide induced by diamide were abolished by capsaicin pretreatment of the guinea pigs. Combined pretreatment with the NK1 and NK2 receptor antagonists, CP-96,345 and SR-48968, attenuated the effect of diamide. Hydrogen peroxide-induced vaso- and bronchoconstriction was not affected by capsaicin-pretreatment, nor did hydrogen peroxide induce detectable release of calcitonin gene-related peptide. The results indicate that diamide activates sensory nerves and induces neuropeptide release and neurokinin receptor-mediated bronchoconstriction in the isolated perfused and ventilated guinea pig lung.

Effect of the thiol-oxidizing agent diamide on NH2Cl-induced rat colonic electrolyte secretion

The granulocyte-derived oxidant, monochloramine (NH2Cl), is known to stimulate chloride ion secretion in rat distal colonic mucosa mounted in Ussing chambers, through mechanisms that are sensitive and insensitive to tetrodotoxin (TTX). The possible role of intracellular thiols, in the mechanism of action of NH2Cl as a secretagogue, was evaluated with the thiol-oxidizing agent diamide and by measuring tissue sulfhydryl levels in response to NH2Cl. Serosal exposure to the antioxidant glutathione (0.25 mM), 5 min before NH2Cl (50 microM) addition, decreased the maximal effect of 50 microM NH2Cl on short-circuit current (Isc). The NH2Cl-stimulated increase in Isc was not affected by mucosal amiloride (5 microM). Pretreatment with 0.1 mM diamide shortened the lag period before the increase in Isc in response to NH2Cl, but it did not affect the maximal increase in Isc. Although TTX (0.5 microM) increased the lag time for achievement of the maximal Isc response to NH2Cl, the neurotoxin did not inhibit the effect of diamide, suggesting that diamide acts primarily on the nonneural component of NH2Cl-stimulated secretion. Incubation of colonic mucosa with NH2Cl, with or without diamide, decreased cellular acid-soluble sulfhydryl concentrations. Taken together, the results support a role for epithelial cell thiols in NH2Cl-stimulated electrolyte secretion by the rat colon.

Reversal by cysteine of the cadmium-induced block of skeletal neuromuscular transmission in vitro

1. Neuromuscular transmission in isolated nerve-muscle preparations was blocked by exposure to Cd2+ for less than 30 min or more than 2 h. The abilities of cysteine, Ca2+ or 3,4-diaminopyridine (3,4-DAP) to reverse the blockade induced by Cd2+ were studied. 2. On the mouse hemidiaphragm preparation, exposure to Cd2+ (10 microM) for 10 to 20 min induced a blockade which was easily reversed by increasing the extracellular Ca2+ concentration (5-10 mM) or by 3,4-DAP (100 microM). Exposure to Cd2+ (3-10 microM) for over 2 h led to a blockade which was not reversed by Ca2+ (5-15 mM) or 3,4-DAP (100 microM). Cysteine (1 mM) was able to reverse completely the blockade induced by both brief and prolonged exposures to Cd2+. 3. In chick biventer cervicis preparations, Cd2+ (100 microM) decreased the twitch height of indirectly stimulated preparations without affecting responses to exogenously applied acetylcholine, carbachol or KCl. Cysteine (1-3 mM) had no appreciable effect on twitch responses to indirect stimulation or to exogenously applied agonists but fully reversed the blockade induced by Cd2+ (100 microM). 4. In mouse triangularis sterni preparations, Cd2+ (1-30 microM) depressed the evoked quantal release of acetylcholine. Concentrations of Cd2+ which completely blocked endplate potentials (e.p.ps) were without significant effect on miniature endplate potential (m.e.p.p.) amplitude and frequency or time constant of decay. Cysteine (1-10 mM) alone had no effect on e.p.ps or m.e.p.ps, but completely reversed the blockade induced by Cd2+.6. In addition to the competitive blocking action of Cd2+ at the prejunctional Ca2+ channels, long exposure to Cd2+ leads to a blockade that is not competitive. This probably involves binding of Cd2+" at an extracellular thiol site on, or close to, voltage-operated Ca2+' channels.

Endo-exocytotic images and changes in synaptic transmission induced by diamide at a cholinergic junction

Small tissue fragments excised from the electric organ of Torpedo marmorata were treated with diamide, a penetrating thiol oxidizing agent, until synaptic transmission was blocked. At this stage, we found an unexpected number of exo-endocytotic images in the presynaptic plasmalemma. Omega-shaped profiles, some of them coated, were seen in thin sections of fixed tissue and pits opened in the P-face of the presynaptic membrane in freeze-fracture replicas from rapidly-frozen preparations. Diamide-treated specimens were frozen at 1 ms time intervals before, during and after a single electrical stimulus. This stimulation did not result in a further increase in the density of presynaptic pits, not in any change affecting the density or size distribution of intramembrane particles. This result is in contrast with what is observed in untreated specimens where transmission of a nerve impulse is accompanied by a momentary rise in the number of large particles. The density of synaptic vesicles--especially that of a subpopulation of small size vesicles--transiently increased within the first 2 h of diamide treatment. During the first stages of intoxication, diamide prolonged the time course of postsynaptic potentials--both spontaneous and evoked--probably by altering the gating properties of receptors (acetyl-cholinesterase activity was not impaired). Later on, all evoked responses were blocked. The spontaneous transmitter release greatly increased, first in the form of quantal miniature potentials. These then subsided whereas a class of very small potentials was generated at a high frequency. Also under the action of diamide, calcium progressively accumulated in the tissue but the number of synaptic vesicles containing calcium deposits was reduced. It is concluded that diamide causes a marked increase in the number of exo-endocytotic images in the presynaptic membrane, suppresses quantal but not subquantal release, and interferes with calcium sequestration in and extrusion from terminals.

Energy metabolism and quantal acetylcholine release: effects of botulinum toxin, 1-fluoro-2,4-dinitrobenzene, and diamide in the Torpedo electric organ

In the Torpedo electric organ, a modified nerve-muscle system, type A botulinum toxin blocked the release of acetylcholine (ACh) quanta, both neurally evoked and spontaneous. At the same time, the toxin increased the release of a class of small miniature potentials (the subminiature potentials), reduced the ATP and more the creatine phosphate content of the tissue, and impaired the activity of creatine kinase (CK). Thus, we compared this pattern of changes with those provoked by 1-fluoro-2,4-dinitrobenzene (FDNB), an efficient inhibitor of CK. As expected, FDNB rapidly inactivated CK, which resulted in a profound depletion of ATP whereas the stores of creatine phosphate were preserved. In addition, FDNB caused conspicuous morphological alterations of nerve endings and ACh depletion. This agent also suppressed evoked and spontaneous quantal release whereas the occurrence of subminature potentials was markedly increased. Diamide, a penetrating thiol oxidizing substance, provoked first a transient rise in quantal ACh release and then blockade of transmission with, again, production of a large number of subminiature potentials. Creatine phosphate was depleted in the tissue by diamide, the ATP content reduced, and CK activity partly inhibited. The morphology of nerve terminals did not show obvious changes with either diamide or botulinum toxin at the stage of transmission failure. Although the three poisons acted by different mechanisms, this resulted in a rather similar pattern of physiological changes: failure of quantal release and enhancement of subquantal release. These results and experiments on synaptosomes indicated that CK inhibition was probably a crucial mechanism for FDNB but not for diamide or botulinum intoxication.(ABSTRACT TRUNCATED AT 250 WORDS)

Phenazine methosulfate induces a neurally-mediated contraction of the guinea-pig ileum

Phenazine methosulfate (PMS) and related phenazines are widely used in biochemistry and histochemistry and act as anti-bacterial agents, however, there is little information on their pharmacological actions. In the present paper the guinea-pig ileum was used as a model for studying the effects of PMS on nerve cells. PMS was found to contract intestinal muscle. This action appeared to be mediated by the activation of muscarinic receptors since it was blocked by atropine. Neostigmine potentiated the response to PMS. The nerve blocker tetrodotoxin prevented the effect of PMS and it is concluded that PMS causes the release of acetylcholine from nerve elements. The action of PMS on nerves is not mediated by nicotinic receptors. Receptors for serotonin, substance P or cholecystokinin also appear not to be involved. Of all the phenazines tested PMS was found to be the most potent and reversible.

The aminoglycoside antibiotic, gentamicin, fails to block increases in miniature endplate potential frequency induced by the sulfhydryl reagent, N-ethylmaleimide, in low calcium solutions

N-ethylmaleimide (NEM) increases the frequency of miniature endplate potentials (MEPPs) at the adult rat hemidiaphragm. This sulfhydryl-alkylating agent produces comparable effects in the absence of added calcium (2 mM EGTA), suggesting that the drug releases calcium from internal stores, or promotes calcium-independent release by depolarizing the nerve terminal or interacting more directly with the release mechanism. These increases in frequency are not blocked by the aminoglycoside antibiotic, gentamicin; although the latter agent reduces quantal content and the elevations in MEPP frequency induced by high potassium solutions. The results suggest that gentamicin and NEM act at different sites at the presynaptic terminal, and that the aminoglycosides block voltage-dependent presynaptic calcium influx.

Characterization of transmitter release as a response of vertebrate neural tissue to erythrosin B

A rat cerebral cortical slice preparation was used to study the response of transmitter release to the application of the food dye, Erythrosin B, a tetraiodinated derivative of fluorescein. Erythrosin B (100 microM) stimulated net release of previously taken up [3H]norepinephrine and [3H]gamma-aminobutyric acid (GABA). The Erythrosin-induced release of GABA (the only transmitter studied) occurred in the absence of added Ca2+, and in the presence of tetrodotoxin (TTX). Ultrastructural analysis of the vesicle content of frog neuromuscular junctions treated with Erythrosin B revealed a diminution in the number of synaptic vesicles present in the nerve terminal. By using fluorescein and some halogen-substituted derivatives including Erythrosin B, it was found that incubation with the unhalogenated compound caused no net release, whereas incubation with the iodine-, chlorine- or bromine-substituted compound did cause release. It was also found that somewhat greater release induced by Erythrosin B (at 100 microM) occurred in the light than in the dark. That Erythrosin B inhibits the Na+,K+,Mg2+-ATPase was confirmed in this preparation; it did so in both light and dark. The discrepancy between release and Na+,K+,Mg2+-ATPase blockade in the dark suggests that release either occurs by some other mechanism than by Na+,K+,Mg2+-ATPase blockade, or that an additional light-dependent process contributes to the release. We conclude that Erythrosin B can presumably induce net release of transmitters generally, that release does not occur via the TTX-sensitive Na+ channel, that release via vesicles does occur, and that light somewhat enhances the release.

Hg2+ causes neurotoxicity at an intracellular site following entry through Na and Ca channels

At motor nerve terminals, Hg2+ causes (a) irreversible depolarization, (b) increase in transmitter release, and (c) subsequent irreversible block of transmitter release. All effects are antagonized when a Na channel blocker (tetrodotoxin, TTX) and a Ca channel blocker (Co2+) are present, but not when either blocker is used alone. The effects are not antagonized by TTX plus Co2+ when the mercurial is lipid-soluble (methylmercury). This indicates that the neurotoxic action of Hg2+ is at an intracellular site and that entry is gained through both Na and Ca channels. The results suggest that metals may inhibit transmitter release at either the Ca channel or at the release site, but that irreversible toxicity is due to an intracellular action, possibly involving SH groups.

Glutathione oxidation in retina: effects on biochemical and electrical activities

This study investigates the possible role of glutathione (GSH) in defending the retina against oxidative damage. Freshly excised rat retina was found to contain 1.2 mumol/g wet wt GSH and an undetectable level of oxidized glutathione (GSSG). Whole retinas were either incubated or superfused with various concentrations of the GSH-oxidant diamide in order to study the effects of oxidation of GSH on the activity of the hexose monophosphate shunt (HMS) and on the receptor potential of the retina. It was found that exposure of the retina to diamide produced a stimulation of HMS activity up to 26-times that of the control. Significant changes in GSH content and receptor potential were observed at concentrations of diamide that produced more than a 5.4-fold stimulation of HMS activity. The diamide-induced electrical alterations included an increase in latency and peak time of the receptor potential, a delay in the onset of the off response and an increase in the time required for the potential to return to the baseline. It was found that nearly 80% of GHS could be regenerated and that most of the electrical effects of diamide could be reversed by superfusion with normal medium. The results indicate that the retina possesses an active system for maintaining GSH in the reduced state and that this may be essential for the normal function of this tissue.

Effects of a thioreactive agent, diamide, on neuromuscular transmission in lobster

Diamide[diazine-dicarboxylic acid-bis(dimethylamide)], a thiol-oxidizing agent, has both pre- and postsynaptic actions on the glutaminergic neuromuscular junction of the lobster walking leg. Postsynaptically, diamide produced an increase in the response to exogenously applied glutamate, whereas the effect of diamide on presynaptic transmitter release involved two major changes: 1) a decrease in excitatory junction potential amplitude and 2) an increase in miniature junction potential frequency. Short-term facilitation also decreased. Equilibration with 1,4-dithiothreitol (a sulfhydryl-reducing agent) reversed the decline in excitatory junction potential frequency, and the fall in short-term facilitation. The miniature junction potential frequency increase induced by diamide was independent of external Ca2+, as diamide in a Ca2+-free solution produced a similar response to that in a Ca2+-containing solution. We propose that the action of diamide on transmitter release is similar to the action of polyvalent cations, i.e., diamide has two sites of action, a blockade of inward Ca2+ flux and an increased release of Ca2+ inside the terminal.

The effect of diamide on transmitter release and on synaptic vesicle population at vertebrate synapses

Diamide, a sulfhydryl-oxidizing agent, has previously been shown to cause acetylcholine release in two preparations in the absence of added Ca2+. Similarities in action between diamide and alpha-latrotoxin, a component of black widow spider venom which causes transmitter release with no added Ca2+, and which seems to require a disulfide bond for its action, led us to study further the transmitter-releasing properties of diamide. In rat cerebral cortical slices we show that diamide, like alpha-latrotoxin, released all transmitters studied; GABA, acetylcholine, norepinephrine and dopamine. The response reached a peak after a delay (5-15 min), in contrast to the much faster release evoked by high K+ (within 3 min). Diamide-induced GABA release was found to occur equally well in the absence of added Ca2+, and was blocked when diamide was reduced prior to addition. Our ultrastructural studies of the frog neuromuscular junction showed that whereas alpha-latrotoxin caused the elimination of synaptic vesicles, diamide did not. Dithiothreitol, a disulfide-reducing agent, also caused GABA release, but this effect was Ca2+-dependent, blocked by high Mg2+, and occurred without delay. These observations comparing the 3 transmitter-releasing agents have further delineated the sulfhydryl/disulfide-group involvement in transmitter release and have demonstrated that dithiothreitol is operating at a different site from either alpha-latrotoxin or diamide.

Diamide, temperature and spontaneous transmitter release at the neuromuscular junction: stimulation of exocytosis by a direct effect on membrane fusion?

The thiol-oxidizing agent diamide markedly increases m.e.p.p. frequency at the frog neuromuscular junction, even at low [Ca2+]0 and also when the mitochondria are uncoupled with DNP. The effect is reversed by dithioerythritol and is very temperature-sensitive, with a marked transition at 16 degrees C; m.e.p.p. frequency is raised 2- to 5-fold at 13-15 degrees C and 55- to 60-fold at 17-20 degrees C. Diamide increases the frequency of large amplitude m.e.p.p.s, the effect being explicable as the fusion of two or more vesicles. It is concluded that (a) diamide does not act at the Ca2+ channels of the plasma membrane, nor at the mitochondria. It affects the release system directly via an alteration of membrane protein --SH groups; (b) the eventual decline in m.e.p.p. frequency after DNP treatment is because of the exhaustion of mitochondrial Ca2+ rather than a depletion of quanta; (c) the major effect of temperature is on the release mechanism, perhaps via a phase-change in the phospholipoproteins of the plasmalemma or vesicles, rather than an elevation of [Ca2+]i; (d) either diamide or temperatures above 16 degrees C make Ca2+ more effective in promoting vesicle-plasmalemma fusion.

Diamide, a sulfhydryl reagent, modifies the light response of Limulus ventral photoreceptors

Responses to light were recorded intracellularly from Limulus ventral photoreceptors during the application of diamide, a sulfhydryl oxidizing agent. At diamide concentrations of over 0.5 mM there was a brief phase of increased response followed by a marked decrease. Diamide also prolonged the response latency, and in several cases increased the frequency of spontaneous discrete waves. At concentrations of 0.25 mM and below, the response only increased. Although the underlying mechanisms of these effects are not understood, these findings may be significant for the understanding of transduction in photoreceptors.

The effect of diamide on amino acid transport by rat renal cortex slices

Diamide directly added to renal cortical slices inhibits the uptake of amino acids. Steady-state kinetic analysis indicates an inhibition of alpha-amino acid influx without effect on efflux. The effect could be reversed by addition of pyruvate to the incubation medium. Although there was a good correlation of the transport effect of diamide with its ability to decrease cellular reduced glutathione concentration, there did not appear to be a necessary connection between them. This was shown by the fact that renal cortical slices stored at 4 degrees C have no alteration in amino acid uptake despite the fact that GSH concentration is as low as that seen with diamide. Diamide was shown to have a direct effect on the uptake of glycine by isolated renal brush border membrane vesicles.

Inhibition of protein phosphorylation and induction of protein cross-linking in erythrocyte membranes by diamide

This report presents studies on the effect of diamide on protein phosphorylation in erythrocyte membranes. Diamide, a thiol-oxidizing reagent, nonspecifically inhibits cyclic Amp-dependent and -independent autophosphorylation of red cell memvranes, but not the activity of the solubilized membrane cycle AMP-independent protein kinases. Analysis of diamide-treated membranes by gel electrophoresis indicates that diamide is capable of inducing cross-linking of membrane proteins. The action of diamide, both in the inhibition of membrane autophosphorylation and in the cross-linking of membrane proteins, is very similar to that of Cu2+. o-phenanthroline complex. Our data indicate that diamide inhibits erythrocyte membrane autophosphorylation by perturbing the protein substrates.

Diamide acts intracellularly to enhance transmitter release: the differential permeation of diamide, DIP, DIP+1 and DIP+2 across the nerve terminal membrane

The actions of the new potent thiol oxidizing agents, diazene dicarboxylic acid bis (N'-methyl piperazide) (DIP) and the N'-methyl iodide (DIP + 1) and the bis-N'-methyl iodide (DIP + 2) salts of DIP, were tested at the frog neuromuscular junction. At 20 degrees C, DIP was as fast as the thiol oxidizing agent, diamide, in evoking transmitter release but was appreciably less effective at 6 degrees C. DIP + 1 and DIP + 2 did not increase transmitter release. Since the three agents are potent oxidizers of glutathione and since the effectiveness of the compounds appears to depend on their ability to exist, at least in part, in a neutral form at physiological pH, it is concluded that their action as promoters of transmitter release depends on their ability to permeate nerve terminal membranes. Thus, both diamide and DIP act to increase transmitter release by the intracellular oxidation of glutathione. The two charged agents, DIP + 1 and DIP + 2, are potent muscular depolarizing agents. It is probable that the quaternary nitrogen groups of these compounds render them cholinomimetics.