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Biomedical subjects

H Ma

Publications and source records attributed to H Ma.

At least 271 records · Page 15Linked to original sources
PubMed1993

Identification of acetylcholine receptors in adult rat trigeminal ganglion neurons.

Nicotinic acetylcholine receptors (nAChRs) were identified in a subpopulation of cultured adult rat trigeminal ganglia (TG) neurons by whole-cell patch-clamp recordings. Dimethylphenylpiperazinium (DMPP), a nAChR agonist, induced inward currents in 21/68 of TG neurons having soma diameters greater than 28 microns. These currents were inhibited by hexamethonium, mecamylamine and atropine, indicating the presence of neuronal ganglionic-type nAChRs. This interpretation is consistent with the finding that the nicotine- or DMPP-induced currents were not inhibited by alpha-bungarotoxin (alpha-Bng) in 5 of the 9 cells tested with this compound. However, in 2 of the 9 cells tested, the DMPP-induced currents were completely inhibited by alpha-Bng, and in the remaining two cells tested, the currents were partially inhibited by alpha-Bng. About 22% of the cells having diameters > or = 28 microns were specifically labeled with FITC-labeled alpha-Bng, whereas only 2% of the cells with soma diameters < 28 microns were labeled. These data taken together suggest that more than one subtype of nAChR is present in TG.

Acetylcholine↗
PubMed1993

Mutagenicity and cytotoxicity of 2-methoxyethanol and its metabolites in Chinese hamster cells (the CHO/HPRT and AS52/GPT assays).

2-Methoxyethanol (ethylene glycol monomethyl ether) (EGME), is one of the most commonly used solvents for industrial and consumer products. Although the solvent has been shown to be a reproductive toxin the genotoxic activities of EGME especially its metabolites, have not been adequately investigated. The mutagenicity and cytotoxicity of EGME and its major metabolites, methoxyacetaldehyde (MALD) and methoxyacetic acid (MAA) in Chinese hamster ovary (CHO) cells were therefore examined by us. We have determined the mutagenicity of these compounds at the hypoxanthine-guanine phosphoribosyltransferase (hprt) locus in CHO-K1-BH4 cells (CHO/HPRT assay) and the xanthine-guanine phosphoribosyl transferase (gpt) locus in CHO AS52 cells (AS52/GPT assay). The results show that these chemicals are not mutagenic to the hprt locus in CHO-K1-BH4 cells either with or without rat liver S9 mix as the metabolic activating system. With AS52 cells, only MALD is mutagenic in the absence of S9. It induced a dose-dependent mutagenic response. A dose-dependent cytotoxicity was induced by all compounds in both cell lines. MALD is the most and EGME is the least cytotoxic compounds. Our study shows that a metabolite of EGME, MALD, is highly cytotoxic and likely induces deletion-type mutations in AS52 cells. The genotoxic effect of EGME is, therefore, dependent upon its metabolism and its detection is dependent upon the assays used.

Animals↗
PubMed1993

Requirement of different subdomains of calpastatin for calpain inhibition and for binding to calmodulin-like domains.

Calpain requires Ca2+ for both proteolysis of its substrates and interaction with its endogenous inhibitor, calpastatin. The mechanism of inhibition of calpain by calpastatin has remained unsolved, although Nishimura and Goll [J. Biol. Chem. 266, 11842-11850 (1991)] reported that autolyzed calpain fragments containing calmodulin-like domains (CaMLDs) bound to an immobilized calpastatin column. We investigated the correlation between CaMLD-binding and calpain inhibition using immobilized columns of gene-engineered CaMLDs derived from the human mu-calpain large subunit and various recombinant calpastatin mutants. Among the four internally repetitive inhibitory domains of calpastatin, each having conserved regions A, B, and C, only domains 1 and 4 showed the binding activity. The region B deletion mutant of domain 1, retaining the CaMLD-binding ability, no longer had the calpain inhibition activity, and became susceptible to proteolysis. In contrast, a synthetic oligopeptide of region B with moderate calpain inhibition activity did not bind to the column. Domain 3 acquired the binding ability on substitution of region A with that of domain 1. These results suggest that calpain inhibition and binding to the CaMLDs are not correlated or mediated by different subdomains of calpastatin.

Amino Acid Sequence↗
PubMed1993

Immunolocalization of the G protein alpha subunit encoded by the GPA1 gene in Arabidopsis.

Heterotrimeric GTP binding proteins (G proteins) are important signal transducers in lower eukaryotes and in animal cells. In plants, the occurrence of GTP binding proteins has been reported, but their biological function remains unclear. Two genes coding for G protein alpha subunits have been cloned: GPA1 in Arabidopsis and TGA1 in tomato. To gain some insights into the function of GPA1, we describe an extensive immunolocalization of GPalpha1, the gene product of GPA1, during Arabidopsis development. Our results show that the GPalpha1 is present through all stages of development and in all organs examined, with the exception of mature seeds. It is expressed in roots, floral stem, rosette leaves, cauline leaves, flowers, and seed pods. Interestingly, the level of GPalpha1 protein is higher in immature organs than in mature organs. GPalpha1 is present at a high level in the root meristem and elongation zone, in the shoot and floral meristems, and in the leaf primordium and floral organ (sepal, petal, stamen, and gynoecium) primordia. During flower development, dividing microspores, but not mature pollen, show high levels of GPalpha1. During pollination, GPalpha1 is present in the growing pollen tubes. The protein is also present in nectaries and developing ovules and, after fertilization, in developing embryos. In mature tissue, GPalpha1 is preferentially found in the vascular system but is also present in other cell types. The complexity of the GPalpha1 localization pattern suggests that GPalpha1 might be involved in different signaling pathways depending on the developmental stage.

Amino Acid Sequence↗
PubMed1993

Calcium entry via L-type calcium channels acts as a negative regulator of adenylyl cyclase activity and cyclic AMP levels in cardiac myocytes.

It is well established that the inotropic effect of beta-adrenergic agonists is mediated by the stimulation of adenylyl cyclase activity and the subsequent phosphorylation of specific proteins by cAMP-dependent protein kinase. The L-type calcium channel is believed to be one of the proteins phosphorylated; the phosphorylation of calcium channels is believed to increase calcium entry into myocytes, which is, at least in part, responsible for the positive inotropic effect. The present studies show that the cAMP-elevating effect of isoproterenol is increased as extracellular calcium is lowered and that calcium channel blockers potentiate the cAMP-elevating effect of isoproterenol in the presence in extracellular calcium. This effect is not dependent on effects on cAMP catabolism and is not specific for beta-adrenergic receptors, because the cAMP-elevating effect of forskolin is similarly affected. Measurements of adenylyl cyclase activity in cardiac membranes show that submicromolar Ca2+ concentrations directly inhibit adenylyl cyclase activity. These results demonstrate that increased entry of Ca2+ via L-type calcium channels in response to beta-adrenergic receptor stimulation acts as a negative regulator of the effect of beta receptor stimulation on adenylyl cyclase activity.

3-Pyridinecarboxylic acid, 1,4-dihydro-2,6-dimethy↗
PubMed1993

[Effect of EA on the enzymes of microvasculature and CA fluorescence in acute myocardial ischemia].

It was aimed at observing the histochemical basis of physiological experiment about the effect of electroacupuncture (EA) on acute myocardial ischemia (AMI) in this paper. The capillaries of myocardium were reflected with both alkaline phosphatase (ALP) and Mg(2+)-ATPase. Thirty min after ligating the left ventricular branch (LVB), the capillaries stained by ALP were much decreased in the ischemic group without EA, while in EA group they were increased distinctly. The number and the total length of the capillaries in a 220 x 320 microns ischemic area of the posterior wall (section 10 microns) were measured and compared. In ischemic group the number was 17.2 +/- 1.65, the length was 634.62 +/- 66.24 microns, in EA group 22.5 +/- 1.44, 1187.57 +/- 103.69 microns, respectively. Both counts were significant differences (P < 0.05, P < 0.001). It reflected that EA could improve the microcirculation and metabolic function of AMI. Mg(2+)-ATPase was shown on the plasma membrane of endothelial cell of microvasculature and analysed quantitatively with a Univar scanning microspectrophotometer. After occluding LVB for 30 min its optic density of AMI was decreased to 106.83 +/- 14.06, while it was increased to 210.83 +/- 24.88 in EA group, P < 0.05. The activity of Mg(2+)-ATPase could increase in transporting Na+, k+ ions through the membrane of the endothelial cells of ischemic myocardium. The result was consistent with the physiological experiment, because EA could regulate the changes of mean repolarization rate induced by AMI and adjust the ion concentration of transmembrane. The catecholamine (CA) in myocardium was located at sympathetic adrenergic terminals with varicosities containing norepinephrine (NE).(ABSTRACT TRUNCATED AT 250 WORDS)

Alkaline Phosphatase↗
PubMed1993

The nutrition transition in China: a cross-sectional analysis.

Diets and activity patterns are changing rapidly in low-income countries, and problems of undernutrition and overnutrition commonly exist side by side. China has conquered problems of food scarcity at the national level and has undergone a remarkable transition in the structure of its diet in the last decade. In this paper, we use data from the 1989 China Health and Nutrition Survey and national data from the State Statistical Bureau to explore China's recent history with respect to nutrition and to identify patterns of under- and overnutrition. In particular, we see that higher income levels, particularly in urban areas, are associated with consumption of a diet higher in fat and with problems of obesity. At the same time, undernutrition is a problem in important segments of Chinese society. There is a need for the Chinese government to consider ways to address these problems of deficit and excess jointly.

Adolescent↗
PubMed1993

Light microscopic radioautographic study on DNA synthesis in aging mice corneas.

The morphological change and DNA synthesis of the aging mice corneal cells were investigated by light microscopic radioautography after injection of tritiated thymidine. The result showed that the incorporation of tritiated thymidine in corneal cells changed with aging. The sites of tritiated thymidine incorporation were located in the epithelium from postnatal day 19 to 1 year after birth, in the stroma and endothelium from prenatal day 19 to postnatal day 8 only. The labeling index in the epithelial cells reached its highest value at 1 month after birth. Labelled stromal and endothelial cells reached their peaks simultaneously on the third day after birth and disappeared completely from postnatal 1 month onwards. The thickness of the cornea increased obviously at one month and there were no notable morphological change thereafter. Our investigation provides for the first time a systematic study on the age-related changes of DNA synthesis and construction in the aging mice corneas.

Aging↗
PubMed1992

Ectopic expression of the floral homeotic gene AGAMOUS in transgenic Arabidopsis plants alters floral organ identity.

The Arabidopsis floral homeotic gene AGAMOUS (AG) is required for development of the reproductive organs (stamens and carpels). In ag mutants, the loss of AG function leads to the conversion of these organs to the perianth organs (petals and sepals). In contrast, mutations in another floral homeotic gene, APETALA2 (AP2), result in the replacement of the perianth organs by the reproductive organs. On the basis of these observations, it has been proposed that AG and AP2 act in an antagonistic fashion. To test this hypothesis, we have studied the effects of ectopically expressed AG in transgenic Arabidopsis plants. The flowers of the transgenic plants exhibit a range of phenotypes mirroring those of ap2 mutants. These experiments provide direct evidence of the proposed antagonism between AG and AP2 functions, and the results strongly suggest that AG does indeed inhibit AP2 function.

Arabidopsis↗
PubMed1992

Manipulation of flower structure in transgenic tobacco.

Genetic studies suggest that three homeotic functions, designated A, B, and C, act alone and together to specify the fate of floral organ primordia in distantly related dicotyledonous plant species. To test the genetic model, we have generated transgenic tobacco plants that ectopically express the AGAMOUS gene from Brassica napus, which is necessary for the C function. Flowers on the resulting plants showed homeotic transformations of sepals into carpels and petals into stamens. These phenotypes are consistent with predictions from the genetic model, show that expression of AGAMOUS is sufficient to provide ectopic C function, and demonstrate that the structure of flowers can be manipulated in a predictable manner by altering the expression of a single regulatory gene. Furthermore, the generation of the predicted transformations by ectopic expression of the Brassica gene in transgenic tobacco indicates that gene functions are interchangeable between phylogenetically distant species.

Amino Acid Sequence↗
PubMed1992

Vectors for plant transformation and cosmid libraries.

A series of vectors has been constructed for the purpose of introducing cloned DNAs into plant genomes, using Agrobacterium tumefaciens-mediated transformation methods. One of these vectors, pCIT20, is a plasmid that contains a multiple cloning site (MCS), and a marker (Hph) that confers hygromycin resistance to plant cells. The others are all cosmid vectors which allow insertion of up to 46 kb of plant genomic DNA, and which also contain all of the necessary sequences for A. tumefaciens-mediated plant transformation. The cosmid vectors either contain a Hph marker (pCIT30), or a kanamycin-resistance marker (pCIT101-104). Three of the cosmid vectors (pCIT30, pCIT101, and pCIT103) carry bacteriophage T7 and SP6 promoters flanking the cloning Bg/II site, for synthesis of end-specific RNAs. The end-specific RNAs may be used as probes when labeled with radioactive or biotinylated nucleotides, for example, in a chromosome-walking experiment. The other two cosmid vectors (pCIT102 and pCIT104) carry restriction sites flanking the insertion site (XhoI) for convenient release of the insert by restriction digests. These sites, in combination with sites internal to the insert, allow the generation of end fragments for subcloning or labeling probes. These vectors should be valuable for isolation and analysis of plant genes, using transformation, library screening, and chromosome-walking approaches.

Agrobacterium tumefaciens↗
PubMed1992

Molecular diversity in amino-terminal domains of human calpastatin by exon skipping.

Calpastatin, a specific inhibitor of calpain, consists of a unique N-terminal domain (domain L) and four repetitive calpain-inhibition domains (domains 1-4). Calpastatin cDNA of human was reported to have two deletions in domains L and 1, as compared with that of pig and rabbit. We isolated human calpastatin genomic DNA clones, and the sequence analysis revealed seven exons for domain L and five exons for domain 1. Those deletions in the human cDNA were retained in its genomic DNA as exons 3 and 11. By the reverse transcription polymerase chain reaction method, three calpastatin cDNAs, full-length domains L and 1, and two natural mutants with deletions in either exon 3 or in both exons 3 and 5, were cloned from human fibroblast WI-38 cell line mRNA. Domain L was found to be rich in basic amino acid residues, especially for exon 3, and its N-terminal half was highly conserved among species. The isoelectric points (pI) of domain L and domains 1-4 were calculated to be 10.27 and 4.26-4.90, respectively. Moreover, human tissues and cell lines displayed different patterns of reverse transcription polymerase chain reaction products in agarose gel electrophoresis. Therefore, alternative splicing is most likely the cause for the molecular diversity, and the multiple isoforms are implicated for specific physiological roles.

Base Sequence↗
PubMed1992

Modulation of cardiac cyclic AMP metabolism by adenosine receptor agonists and antagonists.

The mechanism(s) underlying adenosine receptor-mediated modulation of cardiac cAMP levels has been investigated using detergent-permeabilized embryonic chick ventricular myocytes. The beta-adrenergic receptor agonist isoproterenol (ISO) stimulated adenylyl cyclase activity in detergent-permeabilized cells by 5-10-fold, with an EC50 value of 0.3 microM. Three adenosine receptor agonists, (R)-N6-phenylisopropyladenosine, N6-(3-iodo-4-aminobenzyl)adenosine, and 5'-N-ethylcarboxamidoadenosine, inhibited ISO (10 microM)-stimulated adenylyl cyclase activity in a concentration-dependent manner. The maximum inhibition of the ISO-stimulated adenylyl cyclase activity by (R)-N6-phenylisopropyladenosine (10 microM) was 30-40%. This inhibition was antagonized by the adenosine receptor antagonists xanthine amine congener and 8-cyclopentyl-1,3-dipropylxanthine and was abolished by pertussis toxin treatment, suggesting that the inhibition of adenylyl cyclase activity is mediated by A1 adenosine receptors acting via a pertussis toxin-sensitive guanine nucleotide-binding protein (G protein). Because the adenosine receptor agonists had no detectable effect on phosphodiesterase activity, the adenosine receptor-mediated inhibition of adenylyl cyclase activity appears to account for the cAMP-lowering effect of adenosine receptor agonists seen in intact cardiac myocytes. Moreover, two A1 adenosine receptor antagonists, 8-cyclopentyl-1,3-dipropylxanthine and 3-(4-amino)phenethyl-1-propyl-8-cyclopentylxanthine, stimulated basal adenylyl cyclase activity in the absence of an adenosine receptor agonist; this stimulation was abolished by pretreatment of the cells with pertussis toxin. We postulate that "precoupled" A1 adenosine receptor-G protein complexes, present in the cardiac myocytes, exert a tonic inhibitory influence on adenylyl cyclase activity and that some adenosine receptor antagonists remove this tonic inhibition by destabilizing these precoupled receptor-G protein complexes.

Adenylyl Cyclases↗