Muscarinic acetylcholine receptor-mediated phosphoinositide turnover in cultured cerebellar granule cells: desensitization by receptor agonists

Cultured granule cells prepared from 8-day postnatal rats were used for the study of carbachol-induced phosphoinositide turnover. The addition of carbachol induced a 20- to 30-fold increase in [3H]inositol monophosphate (IP1) accumulation within 30 min in the presence of 20 mM LiCl in granule cells prelabeled with [3H]myoinositol. Carbachol also stimulated the formation of [3H]inositol bisphosphate and [3H]inositol trisphosphate assayed either in the presence or in the absence of lithium; the increase in [3H]inositol triphosphate and [3H]inositol biphosphate synthesis appeared to be faster in the time course but much smaller in amount when compared with the formation of [3H]IP1. The EC50 of carbachol was approximately 7 microM, and the saturation concentration was about 100 microM. This carbachol-induced response was completely blocked by two muscarinic acetylcholine receptor (mAChR) antagonists, atropine and pirenzepine, with a Ki of 0.5 and 120 nM, respectively. Saturation studies of the binding of [3H]N-methylscopolamine and [3H]quinuclidinyl benzilate to mAChRs in intact granule cells revealed the presence of a single class of binding sites with a Kd of 140 and 126 pM, respectively, and a Bmax of approximately 70 fmol/10(6) cells for both ligands. Within 1 hr after pre-exposure of cells to carbachol, the subsequent carbachol-induced [3H]IP1 accumulation was reduced by about 50%, whereas mAChR binding, assessed by using either [3H]N-methylscopolamine or [3H]quinuclidinyl benzilate, was unchanged. A second slower phase of desensitization was associated with a loss of mAChR binding sites; at 18 hr, the decrease of responsiveness was about 80%, whereas the loss of mAChR sites was about 60%.(ABSTRACT TRUNCATED AT 250 WORDS)

Mutagenicity of diesel exhaust particles and oil shale particles dispersed in lecithin surfactant

Diesel exhaust particulate material from exhaust pipe scrapings of two trucks, diluted automobile diesel exhaust particulate material collected on filters, and two oil shale ores were prepared for the Ames mutagenicity assay by dichloromethane (DCM) extraction, by dispersion into 0.85% saline, or by dispersion into dipalmitoyl lecithin (DPL) emulsion in saline. Salmonella typhimurium TA98 was used to detect frameshift mutagens in the samples. Samples of diesel soot gave positive mutagenic responses with both DCM extraction and DPL dispersion, with the DPL dispersion giving higher results in some cases. The results suggest that possible mutagens associated with inhaled particles may be dispersed or solubilized into the phospholipid component of pulmonary surfactant and become active in such a phase.

Gamma aminobutyric acid B receptor-mediated inhibition of adenylate cyclase in cultured cerebellar granule cells: blockade by islet-activating protein

In primary cultures of cerebellar granule cells, the gamma aminobutyric acid B (GABAB) receptor couples to an inhibitory mechanism of adenylate cyclase. The inhibition of adenylate cyclase can be observed either by the measurement of cellular cyclic AMP content or by in vitro measurement of adenylate cyclase from plasma membrane of these cerebellar granule cells. The GABAB receptors can be stimulated by GABA and the GABA analog, baclofen. This receptor-mediated inhibition of adenylate cyclase was blocked by the pertussis toxin, islet-activating protein. Furthermore, the authors show that islet-activating protein catalyzed the ADP ribosylation of the guanine nucleotide inhibitory unit (MW 41,000) in the cerebellar granule cells. In summary, the authors provide evidence supporting the presence of a GABAB receptor in the cerebellar granule cells and suggest that this receptor couples with the guanine nucleotide inhibitory unit to inhibit the formation of cyclic AMP.

Sulphomucin colonic type intestinal metaplasia and carcinoma in the stomach. A histochemical study of 115 cases obtained by biopsy

One hundred fifteen gastroscopic biopsy specimens (54 cases of carcinoma and 61 of gastritis) were used in this histochemical study. Intestinal metaplasia (IM) was classified into small intestinal type (ST) and colonic type (CT). The former may be a reactive change only. The incidence of sulphomucin colonic type (SCT) metaplasia was higher in gastric carcinomas than in benign lesions (P less than 0.01), and a relation between SCT metaplasia and cancer was demonstrated by both histologic and histochemical procedures. This suggests that SCT IM is correlated with certain precancerous lesions. There was no significant difference in the incidence of O-acetyl sialomucin colonic type (OCT) metaplasia between benign and malignant diseases. Further study is needed to determine why slightly more than half of the SCT IM was accompanied by OCT IM.

Sulphomucin colonic type intestinal metaplasia and carcinoma in the stomach. A histochemical study of 115 cases obtained by biopsy

One hundred fifteen gastroscopic biopsy specimens (54 cases of carcinoma and 61 of gastritis) were used in this histochemical study. Intestinal metaplasia (IM) was classified into small intestinal type (ST) and colonic type (CT). The former may be a reactive change only. The incidence of sulphomucin colonic type (SCT) metaplasia was higher in gastric carcinomas than in benign lesions (P less than 0.01), and a relation between SCT metaplasia and cancer was demonstrated by both histologic and histochemical procedures. This suggests that SCT IM is correlated with certain precancerous lesions. There was no significant difference in the incidence of O-acetyl sialomucin colonic type (OCT) metaplasia between benign and malignant diseases. Further study is needed to determine why slightly more than half of the SCT IM was accompanied by OCT IM.

Detection of sister chromatid exchanges induced by volatile genotoxicants

To test the recently developed method of exposing cells to volatile compounds, phytohemagglutinin-stimulated human peripheral lymphocyte cultures were exposed to gaseous methyl bromide, ethylene oxide, and propylene oxide, as well as diesel exhaust. The cultures were placed in sterile dialysis tubing and inserted into enclosed flasks containing additional culture medium. The test compounds (in gaseous state) were diluted with air and bubbled through the flasks for various lengths of time. The cells were then washed and incubated for a total of 75 h. The harvest was performed according to established procedures, and second-division cells were scored for induction of sister chromatid exchanges (SCEs). The SCE frequency was more than doubled in the cultures treated with ethylene oxide and propylene oxide; methyl bromide also induced SCEs. Cultures treated with diesel exhaust showed an increase in the SCE frequency in cells from two of four donors tested. These results further substantiate the use of this method for detecting the induction of SCEs by airborne genotoxins.

Comparative mutagenicity studies of azo dyes and their reduction products in Salmonella typhimurium

The arabinose-resistant and Ames assay systems of Salmonella typhimurium were used to evaluate the mutagenic potential of azo dyes and their aromatic amine reduction products. Azo dyes, namely direct black 38, direct blue 15, and direct red 2, were mutagenic in the arabinose-resistant and Ames assays with both hamster and rat liver S9 activation. Both assays gave relatively higher mutagenic responses with hamster S9. Reduction products of these dyes, namely benzidine, o-dianisidine, and o-tolidine, were mutagenic in the Ames assay. Benzidine was weakly mutagenic and o-dianisidine and o-tolidine were nonmutagenic in the arabinose-resistant assay. These results indicate that both arabinose-resistant tester SV50 and Ames tester TA98 were sensitive in detecting mutagenicity of azo dyes. The use of the standard plate protocol with Ames tester TA98 is more efficient than the modified azo dye protocol in detecting mutagenicity of aromatic amine reduction products. Additional modifications in either the standard plate or modified azo dye protocols may improve detection of mutagenicity of these compounds in the arabinose-resistant assay system.

Arsenic in garden soils and vegetable crops in Cornwall, England: Implications for human health

Total concentrations of arsenic in surface (0-15cm) garden soils in the historical mining area of Hayle-Camborne-Godolphin, Cornwall, England are large and range widely (144-892 μg/g). Amounts of water soluble and acid-fluoride extractable soil arsenic are significantly correlated with total content.Examination of 6 salad and vegetable crops grown in 32 gardens has shown arsenic concentrations in the edible tissues to be only slightly elevated. There were strong correlations between arsenic in beetroot, lettuce, onion and peas and soil arsenic (total, water soluble and acid extractable). Regression equations have been calculated. Ridge regression analysis applied to test the importance of other soil variables has shown both iron and phosphorus to influence the uptake of arsenic.Arsenic in all the vegetables sampled was below the statutory limit in the U.K. of 1 mg/kg fresh weight. Implications for health should be assessed in relation to other exposure routesvia water, air and directly ingested dust and soil.

In vivo cytogenetic studies on mice exposed to ethylene dibromide

The pesticide, ethylene dibromide (EDB), was evaluated with in vivo cytogenetic assays to determine its genotoxicity. CD1 male mice were exposed to EDB through intraperitoneal injections. Bone marrow cells isolated from femora were analyzed for sister-chromatid exchange (SCE), chromosome aberration and micronucleus formation. The results showed that only certain concentrations of EDB tested caused a slight but significant increase in SCEs and chromosome aberrations. However, these increases were not dose-related. No increase in the polychromatic erythrocytes with micronuclei was observed following EDB exposure. Also, EDB did not cause cell-cycle delay in comparison with controls. Thus, it appears that EDB is not an effective genotoxic agent in vivo in mice.

Factors affecting the induction of pollen plants of intergeneric hybrids of Triticum aestivum X Triticum-Agropyron

Experimental results showed that the use of potato extract as a basic component of culture medium had a promoting effect on producing calli in anther culture of the intergeneric hybrids of Triticum aestivum × Triticum-Agropyron (intermediate type). The induction frequencies of pollen callus on the Potato-II medium containing potato extract as the main component was much higher than that found on N6 and W5 media. The induction frequencies of pollen callus and green plantlets in four intergeneric hybrid material inoculated at the late-uninucleate pollen stage were all higher than those inoculated at the mid-uninucleate stage. Appropriate increases in culture temperature significantly increased pollen callus induction frequencies of the intergeneric hybrids. The genotype and physiological state of anther donor plants also influenced pollen callus and green plantlet induction frequencies.

Detection of sister-chromatid exchanges in human peripheral lymphocytes induced by ethylene dibromide vapor

A method using sister-chromatid exchanges (SCEs) for genotoxic testing of gaseous compounds is described. Human peripheral lymphocyte cultures previously stimulated with phytohemagglutinin were placed in sterile dialysis tubing and then put in an enclosed flask containing additional culture media. Air, with or without ethylene dibromide (EDB), was bubbled through the flask for up to 8 h. The cultures were harvested 75 h after culture initiation, and second-division cells were scored for induction of SCEs according to established procedures. The SCE frequency was approximately doubled in cultures treated with EDB. A similar experiment with air alone resulted in only slight increases in SCEs. The results indicate that this system is potentially useful for detecting genotoxicity of gases and vapors and may be useful for the detection of genotoxic agents in occupational settings.

Genotoxic activity of nitrosated coal dust extract in mammalian systems

The genotoxicity of coal dust extract nitrosated by NaNO2 was investigated because of an elevated incidence of gastric cancer in coal miners. Human peripheral lymphocytes were used to determine the frequency of sister chromatic exchanges (SCE) and chromosome aberrations. Chinese Hamster Ovary (CHO) cells were also used to measure SCEs. The mouse lymphoma forward mutation assay comprised the final in vitro system, while the micronucleus test on mouse bone marrow cells was used as an in vivo assay. The SCE frequency in human lymphocytes increased from 9.2 per cell in untreated cultures to 31.6 per cell in cultures treated with 10.0 microliter/ml of nitrosated coal dust extract (NCDE) (P less than .0001). Chromosome aberrations were tested during two phases of the cell cycle; the results indicate that NCDE causes an increase in aberrations in each cell phase tested. The SCE frequency in the CHO system increased from 9.0 per cell in untreated cultures to 18.0 per cell in cultures treated with 3.3 microliter NCDE per ml of medium (P less than .001). In the mouse lymphoma system, the background mutation frequency was tripled at 2.0 microliter NCDE per ml of medium. NCDE was not found to be active in the murine micronucleus assay. No consistent increase in genetic activity was observed with nonnitrosated coal dust extract alone or with NaNO2 alone. Metabolic activation greatly reduced or eliminated genetic activity. These results indicate that nitrosated coal dust extract is genetically active in in vitro mammalian systems without metabolic activation. These findings suggest that the nitrosation of ingested coal dust may be responsible for the elevated incidence of gastric cancer in coal miners.