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Z Q Li

Publications and source records attributed to Z Q Li.

At least 37 records · Page 2Linked to original sources
PubMed1996

Interactions between Ca2+- and cAMP-dependent stimulatory pathways in parietal cells.

Isolated rat parietal cells were used to investigate the role of intracellular Ca2+ in the action of cAMP-dependent secretagogues and cross talk between cAMP- and Ca2+ -dependent stimulatory pathways. Aminopyrine accumulation (an index of acid produced and trapped by the parietal cells), cytosolic free Ca2+, morphological transformation and cell viability were used to investigate parietal cell function and stimulation. The increase of cytosolic free Ca2+ promoted by gastrin, or carbachol, was abolished by the intracellular Ca2+ chelator 1,2-bis(2-aminophenoxy)ethane-N,N,N',N'-tetraacetic acid (BAPTA, 10 microM). Also, the morphological transformations induced by dibutyryladenosine 3':5'-cyclic monophosphate (DBcAMP), gastrin, and Sp-adenosine-cyclic-3', 5'-monophosphothioate (Sp-cAMPS) were completely abolished by BAPTA (10 microM). In aminopyrine accumulation the action of 1 mM DBcAMP was dose-dependently reduced by BAPTA. The Ca2+ ionophore A23187 alone, in the range of 1 pM to 1 microM, had no effect but it dose-dependently potentiated the action of 1 mM DBcAMP in aminopyrine accumulation. The inhibitory actions of BAPTA on DBcAMP- and histamine-stimulated aminopyrine accumulation were dose-dependently reversed by A23187. Histamine-stimulated protein kinase activity and viability parameters as cellular lactate dehydrogenase (LDH) and trypan blue exclusion were not changed by BAPTA. These results indicated that in isolated parietal cells: (1) the action of cAMP-dependent secretagogues in aminopyrine accumulation and morphological transformation are dependent on cytosolic free Ca2+; (2) Ca2+ -induced morphological transformation is essential for aminopyrine accumulation; (3) a threshold level of one second messenger is required for stimulation of aminopyrine accumulation by the other second messenger.

Aminopyrine↗
PubMed1995

Gastrin and carbachol require cAMP to elicit aminopyrine accumulation in isolated pig and rat parietal cells.

The role of endogenous adenosine 3',5'-cyclic monophosphate (cAMP) in the mechanisms of action of gastrin and carbachol on aminopyrine accumulation in isolated pig and rat parietal cells was investigated. In pig cells, pentagastrin (100 nM) alone stimulated aminopyrine accumulation, an action significantly reduced by the protein kinase A inhibitor Rp-adenosine 3',5'-cyclic monophosphothioate (Rp-cAMP[S]; 100 microM). In rat cells, gastrin-17 (100 nM) was incapable of stimulating aminopyrine accumulation, but it potentiated the action of histamine (100 microM). Carbachol (10 microM) stimulated aminopyrine accumulation and potentiated the action of histamine, and its action was potentiated in a dose-dependent manner by Sp-adenosine 3',5'-cyclic monophosphothioate (Sp-cAMP[S]; a cAMP analogue) in both species. The effect of carbachol was dose dependently reduced by Rp-cAMP[S]. The basal cAMP in pig parietal cells was 3.5-fold higher than that in rat parietal cells. Histamine (100 microM) and 3-isobutyl-1-methylxanthine (IBMX; 100 microM) only slightly elevated the cAMP content (1.2- to 2.9-fold the basal level) in both pig and rat parietal cells. Their combination, however, increased the cAMP level by 8- to 38-fold, but it did not increase aminopyrine accumulation above that elicited by histamine alone. Gastrin did not alter the cAMP levels in parietal cells of either of the two species. Both gastrin and carbachol increased cytosolic free Ca2+ in enriched pig and rat parietal cells.(ABSTRACT TRUNCATED AT 250 WORDS)

Aminopyrine↗
PubMed1995

Protection of mice from teratogen-induced cleft palate by exogenous methionine.

A major challenge for biomedical research is the reduction and/or prevention of congenital craniofacial abnormalities which can be induced by some extrinsic toxicants such as retinoic acids (e.g. isotretinoin, Accutane) and glucocorticoids (corticosteroid hormones) during embryonic craniofacial morphogenesis. Our present studies using a genetically susceptible mouse strain (B10.A) indicate that the teratogenic actions of exogenous retinoic acid or glucocorticoid in secondary cleft palate induction can be largely reduced or even completely rescued by subsequent administration of methionine. The greatest reduction in frequency of all-trans retinoic acid- or triamcinolone-induced secondary cleft palate was obtained by a single-dose IP administration of methionine at 187 mg/kg to pregnant mice on E13 21 hr. It appears that detrimental toxic effects were not observed in mice treated with this therapeutic level of methionine. Our present findings support the need for further research into the role of exogenous methionine in cleft palate reduction, that will provide a biological rationale for considering methionine as a therapeutic agent.

Animals↗
PubMed1994

Specific overexpression of P53 in sarcoma derived from Rat-1 cells transformed by cigarette smoking condensate-treated human fetal lung DNA.

The p53 protein is highly expressed in fibrosarcoma derived from Rat-1 cells transfected with cigarette smoke condensate-treated human fetal lung DNA but expressed low in the counterparts of nitroso-N-methylurea and dimethyl sulfoxide groups. Our results denoted that a high expression of p53 protein specifically contributes to the initiation of human lung carcinogenesis induced by cigarette smoke condensate. High expression and missense mutation of p53 may probably be a potential biomarker of initiation of human lung carcinogenesis.

Animals↗
PubMed1994

Effects of vitamins and methionine on blastogenic response of splenocytes and lipid peroxidation in lung and liver of mice exposed to SiO2 dust.

We studied the effects of nutrients such as vitamin C, E, B6, niacin, and methionine on the blastogenic response of splenocytes and lipid peroxidation (LPO) in lung and liver of mice exposed to SiO2 dust. The results showed that after treatment with SiO2, the blastogenic response of splenocytes decreased significantly (p < 0.001), whereas the LPO level in lung and liver increased remarkably (lung p < 0.05; liver p < 0.001). Vitamin E, C, and niacin strongly enhanced the blastogenic response of T and B splenic lymphocytes to concanavalin-A and to lipopolysaccharide (p < 0.001). The effects of methionine and B6 were much less intense. Other supplied nutrients have been shown to inhibit LPO in lung and liver of mice exposed to SiO2 (p < 0.001).

Animals↗
PubMed1994

Inhibition of the transforming ability of cigarette smoking condensate-treated human fetal lung DNA induced by oltipraz.

Rat-1 cells transfected by genomic DNA of human fetal lung explants treated with 100 micrograms/ml of oltipraz (5-(2-pyrazimyl)-4-methyl-1, 2-dithiol-3-thione) for 14 hr or 100 micrograms/ml of cigarette smoking condensate for 6 hr formed 0 to 8 transformation foci, respectively. If 100 micrograms/ml of oltipraz was added to culture of human fetal lung explants 8 hr prior to the treatment of cigarette smoking condensate, the Rat-1 cells transfected by genomic DNA of human fetal lung explants formed only two foci. In addition, the growth speed of Rat-1 cells transfected by genomic DNA of human fetal lung treated with both oltipraz and cigarette smoking condensate was lower than that transfected by cigarette smoking condensate-treated human fetal lung DNA. Our results indicate that oltipraz can block the irreversible change of human fetal lung DNA caused by cigarette smoking condensate, and the results suggest the possibility of using oltipraz as control in the experimental initiation of human lung carcinogenesis.

Animals↗
PubMed1994

The neural retina maintains integrins in the apical membrane of the RPE early in development.

PURPOSE: The retinal pigment epithelium (RPE) lines the interface between the neural retina and the choroid. Early in chicken development, the beta 1 family of integrins resides in the apical (facing the neural retina) and basolateral (facing the choroid) membranes of RPE. Later in development, integrins reside only in the basolateral membranes, which is more typical of simple transporting epithelia. The authors examined whether the distribution of integrins is regulated by the neural retina. METHODS: Individual integrins were examined by studying the individual alpha-subunits that form heterodimers with the beta 1 subunit. The expression and distribution of these subunits were determined by immunoblotting and immunocytochemistry. RESULTS: Subunits alpha 3 and alpha 6 exemplified contrasting behaviors. Early and late in development, alpha 3 was found only in the basal membranes. As was beta 1, the distribution of alpha 6 was nonpolarized early in development but was basal later in development. The effect of the immature neural retina was determined by reconstituting the RPE:neural retinal interface in explant culture. Absent the neural retina, alpha 6 and beta 1 were removed from the apical membrane. When present, the immature neural retina maintained both subunits in the apical membrane. The neural retina was effective only if the outer (primordial photoreceptor) surface of the retina apposed the RPE. CONCLUSIONS: These data suggest that matrix or intercellular interactions determine the distribution of individual integrins. Further, the changes in integrin distribution during development reflect the maturation of the primordial interphotoreceptor matrix or photoreceptor cell layer.

Animals↗
PubMed1993

Gastrin action on aminopyrine accumulation in isolated pig parietal cells requires cAMP.

The mechanism of action of gastrin on pig parietal cells was investigated. The aminopyrine accumulation technique was used to estimate acid production in gastric mucosal cells, containing 10-20% parietal cells, and in enriched parietal cells, containing 65-95% parietal cells. The gastrin analogue pentagastrin stimulated aminopyrine accumulation in a dose-dependent fashion irrespective of the proportion of non-parietal cells present. The apparent EC50 for pentagastrin was 5 nM and the maximally effective concentration was 100 nM. The histamine H2-receptor antagonist ranitidine did not affect the action of pentagastrin. The stimulatory effects of various doses of histamine on aminopyrine accumulation in highly enriched parietal cells were potentiated by the inclusion of 100 nM pentagastrin in the incubation medium. In another series of experiments using mucosal cells, the action of effective doses of pentagastrin were potentiated by the phosphodiesterase inhibitor isobutylmethyl xanthine (IBMX), which alone elicited an aminopyrine accumulation equal to 50% of that obtained by 100 microM histamine. When ranitidine (100 microM) was included, the action of IBMX was almost completely abolished. However, the dose-response curve for pentagastrin in the presence of ranitidine plus IBMX was similar to that obtained in the absence of IBMX. Dibutyryl-cAMP (DBcAMP, 1 mM) in the presence of ranitidine (100 microM) also potentiated the action of all effective doses of pentagastrin on mucosal cells. The protein kinase A inhibitor Rp-cAMPS, present at 500 microM in the incubation medium, significantly reduced the action of each effective concentration of pentagastrin on aminopyrine accumulation in enriched parietal cells. These results in pig parietal cells were interpreted as indicative of: (i) an action of gastrin exerted directly on the parietal cells; (ii) elevation of intracellular cAMP having a permissive role in the action of gastrin on aminopyrine accumulation.

1-Methyl-3-isobutylxanthine↗
PubMed1993

Direct gastrin action on isolated rat parietal cells induces morphological transformations.

In isolated rat parietal cells, a potentiating effect by gastrin of the stimulatory action of histamine and dibutyryl-cAMP (DBcAMP) on aminopyrine accumulation, an index of the acid formed and trapped by the cells, was recently reported by us (1991, Am. J. Physiol. 261, G621-G627). In the present study, this mechanism of action of gastrin was further investigated. Enriched parietal cells (approximately 65% parietal cells) were incubated under different conditions and processed for electron microscopy. Morphometric analysis of the micrographs revealed that pentagastrin (100 nM) was as efficient as histamine (100 microM) in inducing the formation of vacuolar/canalicular spaces in the parietal cells. In the presence of the histamine H2-receptor antagonist ranitidine, histamine was ineffective but pentagastrin and gastrin-17 (G17) maintained their capacity to induce the morphological transformations. By stimulation with pentagastrin plus histamine, the vacuolar/canalicular volume was 2-fold higher than by stimulation separately with each one of the secretagogues. G-17 (100 nM) alone was ineffective but potentiated the maximal [14C]aminopyrine accumulation obtained with 100 microM histamine in mucosal cells (approximately 25-35% parietal cells). Ranitidine blocked both histamine-and histamine plus G-17-stimulated aminopyrine accumulation. G-17 potentiated also the stimulation by 1 mM dibutyryl-cyclic AMP but this was not inhibited by ranitidine. Pentagastrin (100 nM) increased the basal [14C]glucose oxidation in mucosal cells by 30%. This increase was not blocked by ranitidine which, however, abolished the histamine-stimulated glucose oxidation. Incubation of the cells with pentagastrin plus histamine resulted in a glucose oxidation which equaled the sum of the values obtained by each one of the agents. These results indicate that gastrin, acting directly on the parietal cells, potentiates the action of histamine on aminopyrine accumulation by increasing the vacuolar/canalicular spaces, a process that is reflected in the metabolic activity of the cells. Thus a major effect of gastrin at the parietal cell level appears to be the induction of a morphology which is characteristic of stimulated cells rather than a direct activation of ion-transport mechanisms.

Aminopyrine↗
PubMed1993

Messenger RNA phenotyping for semi-quantitative comparison of glucocorticoid receptor transcript levels in the developing embryonic mouse palate.

A specific complex of glucocorticoid and receptor interacts with responsive genes in target tissues of developing palate and controls its morphogenesis. In order to examine developmental changes in glucocorticoid receptor gene expression during embryonic palate formation, variations in transcript levels have been determined using a simple semi-quantitative reverse transcription-polymerase chain reaction (PCR) procedure. Oligo (dT)16 was used as the primer for reverse transcription, and the amount of PCR product for glucocorticoid receptor was normalized against those for glyceraldehyde 3-phosphate dehydrogenase (GAPDH) and beta-actin. We found that either GAPDH or beta-actin were suitable internal standards, and that the mRNA levels of glucocorticoid receptor undergoes a significant decrease of 30% at the developmental stage of embryonic mouse palatal shelf re-orientation. Immunolocalization of the receptor demonstrated a significant change in the distribution pattern of glucocorticoid receptor during the re-orientation stage of secondary palate formation. Our present data suggest that developmental variations in glucocorticoid receptor level control morphogenetic events of secondary palate formation.

Animals↗
PubMed1993

Diffusible, retinal factors stimulate the barrier properties of junctional complexes in the retinal pigment epithelium.

The retinal pigment epithelium lies at the interface between the neural retina and the choriocapillaris where it forms a blood-retinal barrier. Barrier function requires a polarized distribution of plasma membrane proteins and 'tight' tight junctions. During chicken embryogenesis, these features develop gradually. Although terminal junctional complexes are established by embryonic day 4, the distribution of the Na+/K(+)-APTase is not polarized in all cells of the epithelium until embryonic day 11. Similarly, the tight junctions of early embryos are leaky, but become tight by hatching (embryonic day 21). We used primary cell culture to examine the molecular basis of this gradual induction of polarized function. Pigment epithelium harvested from embryonic day 7, and cultured on filters, formed monolayers coupled by junctional complexes. The distribution of the Na+/K(+)-ATPase was non-polarized and the tight junctions were leaky with a transepithelial electrical resistance of 20-30 omega cm2. To isolate diffusible factors that stimulate the transepithelial electrical resistance, neural retinas from embryonic day 7, 14 or 16 embryos were incubated at 37 degrees C in base medium for 6 hours. The conditioned medium was added to the apical chamber of freshly cultured pigment epithelium. The distribution of the Na+/K(+)-ATPase became basolateral, and the electrical resistance gradually increased two to three times over 6 days. The increase in electrical resistance corresponded to a decrease in the rate of [3H]inulin diffusion across the monolayer. The effectiveness of the conditioned medium increased steadily with increasing age of the neural retina. Rather than increased production of an active factor, apparently different active factors were produced at different ages.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1993

[A survey of nutrition knowledge-attitudes-practices of Sichuan urban and rural adults].

To provide a basis for designing nutrition education, two nutrition knowledge--attitudes--practices (KAP) surveys of adults aged 18 to 55 were conducted in 1989 in an urban (N = 1004) and a rural (N = 506) area of Sichuan. The results indicated that the nutrition levels in both sites were low, and an awareness of the relationship between nutrition and certain common diseases was lacking. However, both urban and rural adults possessed good attitudes toward nutrition and nutrition education. Large differences existed between urban and rural adults' food patterns, with the rural diet more monotonous than the urban one. The rural women will be a hard-to-reach audience requiring more intensive efforts. The findings suggest that nutrition education efforts for Sichuan urban and rural area adults will require different contents and emphases, different methods of delivery, and language suitable for each group, in order to obtain good results.

Adolescent↗
PubMed1992

Effects of gastrin on cytosolic free Ca2+ in individual, acid-secreting rat parietal cells.

The effects of gastrin on cytosolic free Ca2+ ([Ca2+]i) in single, isolated rat gastric parietal cells were investigated using the fluorescent probe Fura-2 and digital image analysis. [Ca2+]i was increased by gastrin (100 nM) in approximately 30% of the parietal cells, which were identified by using either the fluorescent probe acridine orange or a parietal cell-specific monoclonal antibody. In the dominant pattern observed, [Ca2+]i was elevated 50-150% and returned within 1-2 min to a value 30-60% over the basal, which was sustained until withdrawal of the stimulant or addition of the gastrin inhibitor L-365,260 (1 microM). The second, but not the first phase, was abolished in the absence of extracellular Ca2+. The results indicate the existence of functional gastrin receptors in a subpopulation of rat parietal cells.

Acids↗
PubMed1991

Theoretical studies on the dihydrofolate reductase mechanism: electronic polarization of bound substrates.

We have applied local density functional theory, an ab initio quantum mechanical method, to study the shift in the spatial electron density of the substrate dihydrofolate that accompanies binding to the enzyme dihydrofolate reductase. The results shed light on fundamental electronic effects due to the enzyme that may contribute to catalysis. In particular, the enzyme induces a long-range polarization of the substrate that perturbs its electron density distribution in a specific and selective way in the vicinity of the bond that is reduced by the enzyme. Examination of the electron density changes that occur in folate reveals that a similar effect is seen but this time specifically at the bond that is reduced in this substrate. This suggests that the polarization effect may be implicated in the reaction mechanism and may play a role in determining the sequence whereby the 7,8-bond in folate is reduced first, followed by reduction of the 5,6-bond in the resulting dihydro compound.

Binding Sites↗
PubMed1991

Changes in the electron density of the cofactor NADPH on binding to E. coli dihydrofolate reductase.

Quantum-mechanical electron density calculations reveal that a significant polarization is induced in the cofactor NADPH (reduced nicotinamide adenine dinucleotide phosphate) on binding to the enzyme dihydrofolate reductase. The calculations indicate that electron density corresponding to approximately 0.7 electron charges is shifted within the molecule, extending over more than 20 A. Further calculations on proposed enzyme mutants show that the polarization of NADPH on binding to DHFR is, in large part, induced by a motif of three positively charged residues. This motif was also identified to be directly responsible for the positive electrostatic potential surrounding the cofactor binding site in the enzyme. The possibility of this long-range polarization of NADPH was originally proposed based on a previous study of ligand binding to DHFR where a conserved structural motif of three positively charged residues was found to play a major role in polarizing the substrate folate over its entire length of 18 A.

Arginine↗
PubMed1991

Characterization of monoclonal antibodies to bovine herpesvirus type I, Los Angeles strain.

We produced monoclonal antibodies (mAbs) against bovine herpesvirus type 1 (BHV-1), Los Angeles strain, and then evaluated them as potential candidates for preparing diagnostic reagents. Of the 318 cell lines expressing antibodies to the virus, 60% (192) secreted IgG and 40% (126) secreted IgM. Twenty-six mAbs were selected based on enzyme-linked immunosorbent assay (ELISA) and virus neutralization (VN) titers and characterized by immunoprecipitation, immunofluorescence and immunoblots. The selected mAbs were assigned to one of four groups based on their immunoprecipitation patterns. Group A (4 mAbs) precipitated a complex of three glycoproteins with molecular weight (MW) 130 kDa, 72 kDa and 55 kDa, which presumably represented gI of BHV-1. Monoclonal antibodies of this group were highly reactive in ELISA but had low VN titers. Group B (4 mAbs) precipitated a glycoprotein with MW of 71 kDa (gIV). This group of mAbs had high VN titers. Group C (16 mAbs) precipitated a 97 kDa glycoprotein (gIII). Monoclonal antibodies of this group had high ELISA but low VN titers. Group D (2 mAbs) precipitated a double band of non-glycosylated proteins with MW of 37/32 kDa; these proteins could not be assigned to any of the antigens of BHV-1 previously described. ELISA and VN titers of this group of mAbs were low. To test the antigenic variability of the antigenic determinants which were recognized by these 4 groups of mAbs, we adapted Madin Darby bovine kidney cell-propagated BHV-1 Los Angeles strain to Crandell's feline kidney cell line. After the tenth passage in feline kidney cells, the epitopes on the 37/32 kDa peptide recognized by the mAbs group D were no longer detectable. Additional changes were noted in the electrophoretic mobility of the 130 kDa and 71 kDa glycoproteins (gI) identified by mAb of group A shifted downward. The 71 kDa glycoprotein (gIV) reactive with mAb group B and the 97 kDa (gIII) reactive with mAb group C remained stable. Since clone No. 191 of group B mAb was potent in ELISA, VN, immunoblots and immunofluorescence, and recognized an epitope which did not change under selective pressure, we feel that the mAb produced by this clone are a good candidate for the production of diagnostic reagents.

Animals↗