Intracellular GTP gamma S restores the ability of morphine to hyperpolarize rat locus coeruleus neurons after blockade by pertussis toxin

The hyperpolarizing effect of morphine on locus coeruleus (LC) neurons, recorded with standard intracellular electrodes, was blocked in brain slices from rats pretreated with pertussis toxin, an inactivator of certain G proteins. In the same slices, when electrodes contained the hydrolysis-resistant GTP analog GTP gamma S, the ability of morphine to rapidly hyperpolarize LC neurons was restored and responses were similar in magnitude to those in control slices. We conclude that there is sufficient residual coupling between opiate receptors and G proteins after pertussis toxin treatment to allow the agonist to be effective when the hydrolysis-resistant GTP analog GTP gamma S is present.

Mutations and homologous recombination induced in mammalian cells by metabolites of benzo[a]pyrene and 1-nitropyrene

Metabolites of two structurally related chemical carcinogens, benzo[a]pyrene and 1-nitropyrene, were compared for their ability to cause cytotoxicity and induce mutations in normally repairing or nucleotide excision repair-deficient diploid human fibroblasts; for their ability to induce mutations in a defined gene sequence, supF, when a plasmid containing adducts formed by these carcinogens replicates in human 293 cells; and for their ability to induce homologous recombination between duplicated genes in mouse L cells. Both of the metabolites tested, i.e., (+/-)-7 beta,8 alpha-dihydroxy-9 alpha,10 alpha, epoxy-7,8,9,10-tetrahydrobenzo[a]pyrene (BPDE) and 1-nitrosopyrene (1-NOP), form adducts on guanine. BPDE binds principally at the N2 position of guanine; 1-NOP binds to guanine at the C8 position. Results of the studies in diploid human cells indicated that when compared on the basis of equal numbers of DNA adducts, BPDE is more effective than 1-NOP in inducing mutations in DNA repair-proficient cells, but when compared in repair-deficient xeroderma pigmentosum human cells that do not remove such adducts from their DNA, the frequency of mutants induced per adduct is equal. These results suggest that during the time available for repair of potentially mutagenic lesions, repair-proficient human cells excise 1-NOP adducts more rapidly than they excise BPDE adducts. Molecular analysis of the specific kinds of mutations induced when a plasmid containing BPDE residues was allowed to replicate in human cells showed that BPDE induces mainly base substitution mutations, predominantly G:C to T:A transversions.(ABSTRACT TRUNCATED AT 250 WORDS)

Common alpha 2- and opiate effector mechanisms in the locus coeruleus: intracellular studies in brain slices

Although alpha 2-adrenoceptor and opiate agonists act through separate receptors on neurons in the locus coeruleus (LC), there are several lines of evidence pointing to shared post-receptor effector mechanisms. Stimulation of either alpha 2- and opiate receptors causes a hyperpolarization of neurons in the locus coeruleus; this effect is due, at least partly, to an opening of a common set of K+ channels. Moreover, the alpha 2- and opiate receptor-induced hyperpolarizations are both reversed, at least partially, by membrane-permeable analogs of adenosine 3':5'-monophosphate (cAMP). These findings fit with biochemical models which propose that alpha 2- and opiate receptors have common actions through inhibiting adenylate cyclase through the inhibitory guanosine triphosphate (GTP) binding protein (Gi). As would be predicted by this model, pretreatment with pertussis toxin, an inactivator of Gi, blocks the hyperpolarizing effects of alpha 2- and opiate agonists in the locus coeruleus. These results suggest that the electrophysiological effects, mediated by these receptors, are transduced through Gi (or a closely related G protein). However, new evidence indicates that there may be both cAMP-dependent and cAMP-independent actions, mediated through G proteins. The opening of K+ channels by alpha 2- and opiate receptors appears to be independent of cAMP, whereas a cAMP-dependent inward current (IcAMP) would be affected by the inhibition of adenylate cyclase; these two G protein-mediated events work in concert to produce the alpha 2- and opiate hyperpolarization of neurons in the locus coeruleus.

Excitation of locus coeruleus neurons by an adenosine 3',5'-cyclic monophosphate-activated inward current: extracellular and intracellular studies in rat brain slices

The firing rate of locus coeruleus (LC) neurons in rat brain slices was increased reversibly by agents that either elevate intracellular levels of adenosine 3',5'-cyclic monophosphate (cAMP) or mimic its actions (e.g., forskolin, and activator of adenylate cyclase, 8-Br-cAMP, a membrane permeable analog of cAMP, and Ro20-1724, a preferential inhibitor of cAMP-phosphodiesterase). Intracellular recordings showed that 8-Br-cAMP and forskolin induce a depolarization of LC neurons, accompanied by a decrease in input resistance. The 8-Br-cAMP- and forskolin-elicited depolarization persisted in the presence of cobalt, a calcium channel blocker. Steady-state current-voltage curves revealed that in the voltage range of -50 to -120 mV, 8-Br-cAMP and forskolin induced an inward current, which did not reverse at the potassium equilibrium potential and could not be blocked by tetrodotoxin. Partial replacement of sodium with Tris or choline markedly reduced the depolarization elicited by 8-Br-cAMP. We conclude that 8-Br-cAMP and forskolin act through a common mechanism to increase the firing rate of locus coeruleus neurons by inducing a cAMP-activated inward current, carried out at least in part by sodium ions.

Disubstituted amino-, nitroso-, and nitrofluorenes: a physicochemical basis for structure-activity relationships in Salmonella typhimurium

Twenty-nine derivatives of fluorene were tested for mutagenic potency in four strains of Salmonella typhimurium with and/or without S9 microsomal activation. The effects of a second functional group on the mutagenic activity of an amino-, nitroso-, and nitrofluorene were correlated with its physical and chemical properties. When the functional group is conjugated by resonance, both inductive and resonance effects are determinants of mutagenic potency. Electron-withdrawing groups such as the halogens (F, C1, Br, and I), nitro, nitroso, and cyano at C-7 increased the mutagenic potency of 2-nitrofluorene. Electron-donating substituents such as hydroxy and amino groups at C-7 decreased the mutagenic potency of 2-amino, 2-nitroso-, and 2-nitrofluorene. Acetylation of a hydroxy or an amino group at C-7 increased the mutagenic potency of 2-nitrofluorene, presumably by decreasing the electron-donating properties of these groups. In contrast, acetylation of a nonresonance-conjugated amino group decreased mutagenic activity. The physical properties of a second functional group are expected to exert their effect(s) at three points in the metabolic activation of 2,7-disubstituted fluorene derivatives: initial reduction of the nitro group (redox effect), stabilization of the hydroxylamine (inductive effect), and stabilization/destabilization of the nitrenium ion (resonance and inductive effects). The relationships between the physical properties of a second functional group and their effects on biological activities of nitro- and aminofluorenes in the Ames Salmonella assay may be of predictive value in a first approximation of both the mutagenic and carcinogenic potency of chemicals with comparable structures such as fluoranthene and biphenyl.

Pertussis toxin blocks the outward currents evoked by opiate and alpha 2-agonists in locus coeruleus neurons

Pertussis toxin, a substance known to inactivate the inhibitory guanine nucleotide regulatory unit of adenylate cyclase, was injected into the lateral cerebral ventricle of rats; intracellular recordings were made from locus coeruleus neurons in brain slices 1-3 days later. Morphine (an opiate agonist) and clonidine (an alpha 2-agonist) produced the expected outward currents (and associated hyperpolarization and inhibition of firing) in controls whereas the effects of both agonists were blocked in animals pretreated with pertussis toxin. These results are consistent with the hypothesis that opiate and alpha 2-agonists may depress the firing of locus coeruleus neurons by inhibiting adenylate cyclase via a guanine nucleotide regulatory protein.

Structure-activity relationships of nitro and methyl-nitro derivatives of indoline, indole, indazole and benzimidazole in Salmonella typhimurium

The mutagenic activities of eleven nitro derivatives and eleven N-methyl-nitro derivatives of indoline, indole, indazole and benzimidazole were investigated in Salmonella TA98 and TA100. The presence of a nitro group at C4 or C7 resulted in only weakly or nonmutagenic compounds, while a nitro group at C2, C5 or C6 usually resulted in measurable mutagenic activity in the non-N-methylated compounds. Methylation of a ring nitrogen usually reduced the mutagenic activity of these nitroheterocyclics except 2-nitro-benzimidazole, which resulted in a better than 300-fold increase in mutagenic activity. A proposed mechanism for the increased mutagenic activity obtained by methylation of imidazole nitrogens may provide insights into the reasons for the potent mutagenicities observed for several similarly methylated cooked-food mutagens.

Improvement in hearing among otherwise normal schoolchildren in iodine-deficient areas of Guizhou, China, following use of iodized salt

According to a survey in Guizhou province of China, the average hearing level of otherwise normal schoolchildren in an area of endemic iodine-deficient goitre and cretinism was significantly poorer than in a non-endemic control area. After iodine prophylaxis for three years, audiometric tests showed that the average hearing level had improved and approached that of the non-endemic controls. In addition, mean values for thyroid function tests were restored to within the normal range. It is suggested that the most likely cause of the poorer hearing level among the ostensibly normal schoolchildren in endemic areas is subclinical hypothyroidism due to prolonged severe iodine deficiency.

Formation of mutagens in cooked foods. V. The mutagen reducing effect of soy protein concentrates and antioxidants during frying of beef

Cooking beef patties results in the formation of mutagens detectable by Salmonella typhimurium TA98 with metabolic activation. Decreased mutagenic activity results when frying beef with added soy protein concentrates (SPC). The reduction in mutagenicity takes place during the cooking process. Whereas fried beef hamburgers show high mutagenic activity, by comparison, similarly fried soy-hamburgers have much less mutagenic activity. Volumetric effects are responsible partly for the reduction on mutagenicity by SPC. Naturally occurring antioxidants in SPC, such as chlorogenic acid, also play a role. Also, a commonly used antioxidant, butylated hydroxyanisole (BHA), has been found effective in reducing the mutagenicity of fried beef. Thus, the addition of SPC or BHA in beef patties may provide a practical way of reducing mutagen formation during frying of beef.

Enhancement of formation of the esophageal carcinogen benzylmethylnitrosamine from its precursors by Candida albicans

Previous studies in Linxian, an area of China with a high incidence of esophageal carcinoma, showed that fungal infections are common in the esophageal epithelium of patients with either premalignant changes or early esophageal carcinoma. Fungi of the genus Candida were the most frequent invaders. In these areas nitrate and nitrite are often present in high concentrations in drinking water and staple grains. The present studies have established the ability of Candida albicans to augment the nitrosative formation of the esophagus-specific carcinogen, benzylmethylnitrosamine (NBMA; N-nitroso-N-methylbenzylamine). Stationary C. albicans cultures, with pH held at 6.8, were incubated with the precursors of NBMA, benzylmethylamine (BMA; N-methylbenzylamine) and NaNO(2). There was a significant increase in the amount of NBMA formed in these cultures, compared to precursors-only controls. The amount of NBMA synthesized depended on fungal cell number. Exponentially growing cultures were also able to cause NBMA formation. The identity of the NBMA was confirmed by high-performance liquid chromatographic coelution with authentic NBMA in three solvent systems and by mass spectroscopy. Boiled cells and conditioned medium in which cells had been incubated were not effective in enhancing nitrosation. Cultured Candida released acidic metabolites that reduced the pH of the medium when only a low concentration of buffer was present. Spontaneous nitrosation of BMA was enhanced under these acidic conditions. Thus, C. albicans infecting the esophageal epithelium could cause local formation of NBMA by both cell-mediated catalysis and extracellular decrease in pH.

Antimutagenic properties of liver homogenates, proteins and glutathione on diesel exhaust particulates

Diesel exhaust particulates contain mutagens which are active in the Ames Salmonella typhimurium assay. The mutagens do not require liver enzymes for activation and, in fact, the addition of liver homogenates (S-9) to the Ames system decreases the mutagenicity of diesel exhaust samples. We have examined here the properties and components of S-9 that account for its antimutagenic effect. The antimutagenic effect of S-9 is not changed by heating S-9 in a boiling water bath for 5 min or by omission of the NADPH-generating system in the cofactor mixture. These experiments showed that the antimutagenic effect on S-9 is not enzymatic. The antimutagenicity of S-9 disappeared after the protein component of S-9 was removed by filtration. Exogenous albumin added to the Ames system mimicked the antimutagenic effect. Analysis of the albumin content of liver cytosol showed that 90% of the antimutagenic effect could be accounted for by the amount of albumin present. Glutathione added to diesel exhausts reduced mutagenicity, but the qualities of glutathione present in S-9 are too small to account for the antimutagenic effect of S-9. We conclude that the antimutagenic effect of S-9 is non-enzymatic and is most likely the result of non-specific protein binding of mutagens to liver albumin. The antimutagenic effect of glutathione on diesel exhausts suggests that the mutagens present are electrophiles.

Seizure disorders and trace metals: manganese tissue levels in treated epileptics

We determined the concentrations of manganese in whole blood and hair in 52 epileptics, 6 blood relatives, and 24 normal controls. Blood, and possibly hair manganese content, was significantly lower in treated epileptics than in controls (p less than 0.002). Although not all patients showed reduced tissue manganese levels, most of those with frequent seizures had manganese levels falling below the lowest control level, suggesting a relationship between manganese tissue levels and high seizure activity. These differences in manganese levels were not correlated with the type, dose, or plasma levels of anticonvulsant medication. Reduced manganese availability at the neuronal level, where Mn++ stabilizes membrane excitability, may affect epileptogenic lesions to increase the likelihood of seizure activity.

Protein quality of several multi-component, commercially prepared foods

Eleven commercial food products that may be considered by consumers to be major sources of protein were evaluated. Most of these items contained significant amounts of carbohydrate in the form of cereal products or purified sugars. Seven of the products were at least equal to casein in protein efficiency ratio (PER). Canned spaghetti and meat balls, the TV dinner, canned chicken-and-vegetable baby food, and food bars had PER values between 91 and 73 per cent of that of casein, while PER values for ground beef and high-protein cereal were significantly higher than casein.

On the correlation between rast and the allergy intradermal test

RAST and intradermal testing correlated reasonably well for untreated patients for ragweed and molds and in treated patients for trees. Capillary blood was found to be comparable to venous blood as a source for RAST for ragweed and mixed grasses.

Plasma DOPA and growth hormone in parkinsonism: oscillations in symptoms

In 19 patients with Parkinson disease, we studied the relationship of the therapeutic effect of levodopa, or dyskinesia, to the plasma content of DOPA and growth hormone (GH). Those with stable responses to levodopa, individually or as a group, showed stable and lower plasma DOPA levels than those with unstable symptomatic responses. These results show that stable and oscillating clinical responses in Parkinson disease parallel plasma DOPA levels, suggesting that there are different mechanisms in peripheral levodopa metabolism and that extracerebral mechanisms are important in regulating the availability of levodopa to the brain. Plasma GH did not differ in the two groups, suggesting that the secretion of GH is independent of the effects of levodopa in parkinsonism.

Direct-acting mutagens in automobile exhaust

Particulate matter in city air contains chemicals which are mutagenic in the Ames Salmonella typhimurium assay. In residential urban areas, the principal mutagens in air do not require liver enzymes to be activated. The source of these liver independent (direct-acting) mutagens may be automobile exhaust because (1) the mutagenic activities were correlated to the lead content or air, (2) the mutagens were found exhaust samples from automobiles and from an experimental CFR single-cylinder gasoline engine, and (3) these mutagens were not found in fuel or unused motor oil, but were found in used motor oil. The strain specificity and the fact that liver enzymes were not required for activation indicated that the exhaust and airborne mutagens were not unsubstituted polycyclic aromatic hydrocarbons (PAH), aromatic amines, alkylnitrosamines or aliphatic epoxides, peroxides and hydroepoxides. A number of nitro-substituted aromatic compounds are direct-acting mutagens in the Ames test, and it is possible that nitration of PAH in exhaust may form the compounds observed here. We synthesized 6-nitrobenzo [a] pyrene and found it to be a potent, direct-acting mutagen with activity comparable to that of benzo-[a] pyrene.

An Ascorbate-induced Absorbance Change in Chloroplasts from Violaxanthin De-epoxidation

A new ascorbate-induced chloroplast absorbance change which has the characteristics of a carotenoid shift is described. The absorbance change was light-dependent at pH 7 but not at pH 5. The difference spectra for the light and dark changes were similar, showing a large absorbance peak at 505 nanometers, smaller peaks near 468 and 437 nanometers, and a sharp valley around 483 nanometers. The absorbance change is assigned to violaxanthin de-epoxidation because various conditions affected the absorbance change and violaxanthin de-epoxidation similarly, and the difference spectrum resembled the spectrum of zeaxanthin minus violaxanthin in organic solvent.Nigericin with KCl inhibited the light-dependent change at 505 nanometers. This effect, as well as the dark change at pH 5, indicated that de-epoxidation requires an acidic condition in chloroplasts. The effects of 3-(3,4-dichlorophenyl)-1, 1-dimethyl urea, 2,6-dichlorophenolindophenol, and phenazine methosulfate indicated that the chloroplast acidification which mediates the 505 nanometers change is derived from hydrogen-ion transport linked to photosystem 1. Thus the 505 nanometers change could serve as an endogenous probe for chloroplast acidification and an indirect indicator of hydrogenion transport. At pH 5, the role of ascorbate appears to be to provide the reducing potential necessary for reductive de-epoxidation of violaxanthin. At pH 7, ascorbate could have an additional effect of stimulating electron transport and hence the hydrogen-ion transport necessary for de-epoxidation.In contrast to leaves and algae, de-epoxidation in chloroplasts was irreversible under the conditions investigated. Under some conditions other absorbance changes which were apparently due to chlorophyll were superimposed on the de-epoxidation change. The relationship of these ascorbate-induced changes to other absorbance changes observed in chloroplasts and green algae remains to be determined.