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C Du

Publications and source records attributed to C Du.

At least 109 records · Page 6Linked to original sources
PubMed1995

[Establishment of three-dimensional finite element models by using a series of plane section images processed with an image analysis system].

The geometric similarity and mesh dividing of finite element models directly create an effect on the results of analysis when a theoretical stress analysis is performed by the use of finite element method. The model is routinely established by means of sectioning the specimen. In this paper, a series of plane section CT images of the teeth and mandible, an image analysis system and a specially designed software for modeling three-dimensional finite element were used to establish a three-dimensional finite element model. It is a new preprocessing method for finite element applications in the field of oral biomechanism. The technique is characterized by the advantages of high similarity of the model to specimens and no damage to specimens; it is simple and easy. The images and figures can be repetitively used.

Biomechanical Phenomena↗
PubMed1995

Therapeutic efficacy of paromomycin in immunosuppressed adult mice infected with Cryptosporidium parvum.

The intent of this study was to evaluate the therapeutic efficacy of paromomycin in immunosuppressed adult C57BL/6N mice infected with Cryptosporidium parvum. Seven groups of 10 mice/group were used. Groups 1, 2, and 7 served as normal, toxicity, and placebo controls, respectively. Groups 2-7 were immunosuppressed with dexamethasone phosphate administered ad libitum in drinking water. Groups 3-7 were infected with C. parvum on day 7 postimmunosuppression. Groups 3-6 were treated by administering paromomycin per os for 10 consecutive days, beginning on day 10 postinfection, at dosage levels of 0.25, 0.5, 1, and 2 g/kg/day, respectively. Paromomycin was judged to be nontoxic at the dosage levels used. Groups 1 and 2 remained uninfected while groups 3-7 began shedding oocysts by day 3 postinfection. Paromomycin was therapeutically effective against C. parvum at 1 and 2 g/kg/day as determined by significant reductions in fecal oocyst shedding (P < 0.01), parasite colonization (P < 0.05), and villus atrophy (P < 0.05) in the ilea and terminal ilea of infected mice. We conclude that paromomycin may be useful in the treatment and palliation of cryptosporidiosis.

Animals↗
PubMed1995

[Determination of sterigmatocystin in cancerous tissues, blood and urine in patients with liver and stomach cancer].

Sterigmatocystin (ST) was determined with modified Southern-Western blot and indirect competitive enzyme-linked immunosorbent assay (IC-ELISA) for 28 specimens of cancerous tissues, 13 of blood and 20 of urine in 14 patients with liver and stomach cancer. Results showed DNA-ST adduct was detected in 14 specimens of cancerous tissues and/or pericancerous tissues. ST values were higher in four of 13 patients (65-113 micrograms/kg), as compared only in one of 14 healthy persons (68 micrograms/kg). And, ST values all were very low in urine, with a maximum of 13 micrograms/kg.

DNA Adducts↗
PubMed1995

[The correlation between changes of static central visual fields and posterior polar lesions in high myopia].

The static central visual fields tested by an Octopus Field Analyzer and posterior polar lesions in 53 cases with high myopia were investigated. Cases with low and moderate degrees of myopia were the controls. The results demonstrate that the visual field defects are present in the high myopic eyes and they are related to the degree of high myopia, the age of the patient and the severity of the posterior polar lesion. The visual field defects present multiform and multilevel in character and they do not completely correspond to the fundus lesions. The appearance of central relative scotomata in high myopic eyes detected by a quantified automated perimeter is prior to the appearance of macular lesions seen under an ophthalmoscope. Therefore, the quantified automated central visual field examination is helpful to the early diagnosis of macular disease in high myopia.

Adolescent↗
PubMed1994

Comparison of Disulfide Contents and Solubility at Alkaline pH of Insecticidal and Noninsecticidal Bacillus thuringiensis Protein Crystals.

We compared two insecticidal and eight noninsecticidal soil isolates of Bacillus thuringiensis with regard to the solubility of their proteinaceous crystals at alkaline pH values. The protein disulfide contents of the insecticidal and noninsecticidal crystals were equivalent. However, six of the noninsecticidal crystals were soluble only at pH values of >/=12. This lack of solubility contributed to their lack of toxicity. One crystal type which was soluble only at pH >/=12 (strain SHP 1-12) did exhibit significant toxicity to tobacco hornworm larvae when the crystals were presolubilized. In contrast, freshly prepared crystals from the highly insecticidal strain HD-1 were solubilized at pH 9.5 to 10.5, but when these crystals were denatured, by either 8 M urea or autoclave temperatures, they became nontoxic and were soluble only at pH values of >/=12. These changes in toxicity and solubility occurred even though the denatured HD-1 crystals were morphologically indistinguishable from native crystals. Our data are consistent with the view that insecticidal crystals contain distorted, destabilized disulfide bonds which allow them to be solubilized at pH values (9.5 to 10.5) characteristic of lepidopteran and dipteran larval midguts.

Journal Article↗
PubMed1994

Detection of point mutations in exon 2 of the G6PD gene in Chinese G6PD variants.

In the past few years, a total of 6 different mutations of the G6PD gene have been reported in China. One of these, the C6 mutation (A95-->G), accounted for about 15.4% of the Chinese G6PD variants. In order to develop a strategy for rapid detection of mutation-containing exons of the G6PD gene, we applied the single-strand conformation polymorphism (SSCP) technique to the detection of mutations in exon 2 of this gene. We observed four patients with abnormal migration patterns of the exon 2 band among 20 cases of G6PD variants. Direct PCR sequencing confirmed a T to C substitution in exon 2 that has previously been reported. This procedure is therefore of particular importance for the rapid detection of mutation-containing exons in the G6PD gene.

Base Sequence↗
PubMed1994

Mechanism of cyclic AMP-induced hyperpolarization in canine colon.

The mechanism of forskolin (FSK)-induced hyperpolarization was investigated in strips of canine colonic circular muscle. FSK responses were compared to those of the K+ channel opener lemakalim (LEM). Both FSK (10 microM) and LEM (10 microM) hyperpolarized cells near the myenteric border by 10 to 20 mV. Responses to both agents were abolished by 35 mM external K+, indicating a probable mediation by K+ channels. FSK increased the open probability of Ca(++)-activated K+ channels in isolated colonic myocytes. However, in muscle strips charybdotoxin (100 nM) and tetraethylammonium (10 mM) failed to reduce FSK- and LEM-induced hyperpolarizations whereas tetrapentylammonium (50 microM) and 4-aminopyridine (10 mM) blocked both responses. Phencyclidine (100 microM), Ba++ (1 mM) and the antagonist of ATP-sensitive K+ currents glybenclamide (10 microM) blocked LEM- but not FSK-induced hyperpolarizations. Delayed rectifier current in isolated myocytes was activated near -20 mV and was blocked by (order of potency): nifedipine > tetrapentylammonium > phencyclidine > 4-aminopyridine > tetraethylammonium. Charybdotoxin (100 nM), Ba++ (1 mM) and glybenclamide (10 microM) were without effect. Ca(++)-activated K+ current was activated near +30 mV and was blocked by: charybdotoxin > tetraethylammonium > tetrapentylammonium >> phencyclidine = 4-amino-pyridine. These data suggest that LEM induces membrane hyperpolarization by activation of a K+ current with a pharmacology similar to ATP-sensitive K+ current whereas cyclic AMP-induced hyperpolarization appears to involve activation of a current other than delayed rectifier current, Ca(++)-activated K+ current or ATP-sensitive K+ current.

Animals↗
PubMed1993

Characterization and mediation of inhibitory junction potentials from opossum lower esophageal sphincter.

BACKGROUND: Activating nonadrenergic, noncholinergic (NANC) nerves of the lower esophageal sphincter (LES) hyperpolarizes and relaxes its circular smooth muscle. This relaxation is mediated by nitric oxide (NO) or an NO-containing compound. These studies were undertaken to compare the electrophysiological responses of circular smooth muscle from the LES and esophagus in response to NANC nerve stimulation and to test the hypothesis that NO mediates LES hyperpolarization. METHODS: The transmembrane potential difference was recorded with glass microelectrodes. Nerve-mediated membrane responses were evoked by electrical pulses of 0.5 msec duration and 50 V amplitude. RESULTS: Responses of LES muscle differed from those of the esophageal muscle. The duration of hyperpolarization was much longer in sphincteric muscle. The depolarization that followed hyperpolarization of esophageal muscle was not observed in sphincteric muscle. NG-nitro-L-arginine, an inhibitor of NO synthase, attenuated the nerve-induced hyperpolarization. L-arginine, the substrate for NO synthase, antagonized the effect of NG-nitro-L-arginine. Exogenous NO hyperpolarized of the smooth muscle membrane. CONCLUSIONS: These data support the hypothesis that NO or an NO-like compound may mediate nerve-induced hyperpolarization of the opossum LES.

Animals↗
PubMed1993

Enteric inhibitory neural regulation of human colonic circular muscle: role of nitric oxide.

BACKGROUND: Nitric oxide and an apamin-sensitive transmitter may both contribute to neural inhibition in the human colon. The present study investigated the role of NO in regulating spontaneous rhythmic contractions and examined NO-dependent and independent components of neurally evoked hyperpolarization in the human colon. METHODS: Mechanical and electrical activity were recorded from isolated circular muscle strips. RESULTS: Rhythmic contractions were inhibited by nerve stimulation. This response was reduced by apamin, oxyhemoglobin, and L-NG-nitro arginine methyl ester (L-NAME). Electrical recording revealed two components of neurally evoked hyperpolarization: a fast hyperpolarization resulting from a single stimulus and a sustained hyperpolarization that developed with repetitive stimulation. Fast hyperpolarization was not affected by L-NAME or oxyhemoglobin but was significantly reduced by apamin. The sustained hyperpolarization was reduced by L-NAME or apamin. Exogenous NO and the P2y receptor agonist 2-methylthio adenosine 5'-triphosphate (2-MATP) inhibited spontaneous contractions and produced hyperpolarization. Apamin reduced the effects of 2-MATP but not those of NO. CONCLUSIONS: The results support the concept that the inhibitory neurotransmission in the human colon involves two transmitters. A single stimulus results in an apamin-sensitive response. With multiple stimuli, a NO-dependent response develops and sums with the apamin-sensitive mechanism, producing sustained hyperpolarization and inhibition of contractions.

Action Potentials↗
PubMed1992

Guanylate cyclase inhibitors: effect on inhibitory junction potentials in esophageal smooth muscle.

Electrical field stimulation (EFS) of nerves intrinsic to the opossum lower esophageal sphincter (LES) produces LES relaxation, an increase in its guanosine 3',5'-cyclic monophosphate (cGMP) content, and hyperpolarization of its circular muscle membrane potential difference. Activation of esophageal nerves produces an analogous hyperpolarization of the circular esophageal smooth muscle. These studies test the hypothesis that cGMP is an intracellular mediator of this hyperpolarization. The transmembrane potential difference of circular smooth muscle cells was recorded with glass microelectrodes. Nerve-mediated smooth muscle hyperpolarization was evoked by EFS (1 ms, 50 V pulses). Forskolin, an activator of adenylate cyclase, and sodium nitroprusside, an activator of guanylate cyclase, produced hyperpolarization. Cystamine and methylene blue, inhibitors of guanylate cyclase, blocked the hyperpolarization elicited by sodium nitroprusside, but not that by forskolin. Both also reversibly abolished the hyperpolarization evoked by EFS. Membrane-permeable derivatives of cGMP produced a concentration-dependent hyperpolarization. These data support the hypothesis that cGMP is an intracellular mediator of nerve-induced esophageal smooth muscle hyperpolarization.

Animals↗
PubMed1992

Guanylate cyclase inhibitors: effect on tone, relaxation, and cGMP content of lower esophageal sphincter.

Relaxation of the lower esophageal sphincter (LES) results from activation of its intrinsic innervation. This relaxation is associated temporally with an increase in the guanosine 3',5'-cyclic monophosphate (cGMP) content of the muscle. This study tests the hypothesis that variations in the production of cGMP mediate resting LES tone and nerve-induced relaxation. We examined the effects of guanylate cyclase inhibitors, such as cystamine and methylene blue (MB), on the resting tone, resting membrane potential, electrical field stimulation (EFS)-induced relaxation, and cGMP content of circular smooth muscle from the LES of the opossum. Strips of sphincter muscle were placed in a tissue bath and stretched to 125% resting length. Both cystamine and MB increased the resting tone of LES muscle in a concentration-dependent manner (EC50 = 1.1 +/- 0.2, n = 12, and 1.6 +/- 0.4 mM, n = 10, respectively). The increase in tone by cystamine was not blocked by tetrodotoxin, atropine, or propranolol. Cystamine (1 mM) did not alter the resting membrane potential of circular muscle cells of the LES. The removal of extracellular Ca2+ by the addition of ethylene glycol-bis(beta-aminoethyl ether)-N,N,N',N'-tetraacetic acid (EGTA, 4 mM) and nifedipine (1 microM) shortened the duration but not the amplitude of the response to cystamine. Pretreatment with caffeine (5 mM) in the presence of EGTA and nifedipine to deplete intracellular Ca2+ stores blocked the increase in tone by cystamine. Cystamine (1 mM) failed to inhibit LES relaxation induced by EFS. Carbachol, at a concentration that induced a similar increase in base-line tone, attenuated the nerve-mediated relaxation. Cystamine did not alter basal cGMP levels, but inhibited the rise in cGMP induced by EFS. The data indicate that cystamine increases LES tone but does not inhibit EFS-induced relaxation, even though it inhibits EFS-induced increases in cGMP content. The increase in tone is dependent on the presence of intracellular Ca2+ stores.

Animals↗
PubMed1992

[Studies of the relationship between transferrin genetic polymorphism and diseases].

Genetic polymorphism of transferrin (Tf) was investigated in Han nationality population in Guangzhou area using isoelectric focusing technique. In addition, three diseases (Leukaemia, Heptocarcinoma, Systemic-lupus-erythematosis, SLE) were also typed for Tf and compared with that in normal population. The increased TfC1 gene frequency in acute myelocytic leukaemia (AML) patients was found (chi 2 = 4.16, P less than 0.05). The increased frequency of TfC1C1 was also observed (P less than 0.05). Relative Incident(RI) was 1.9 But TfC1 gene and TfC1C1 phenotype frequencies did not increase in ALL, CML and primary heptocarcinoma patients. It suggests that TfC1 may relative to AML in this area. Besides, the increased TfC1 gene frequency was observed in SLE patients (chi 2 x 6.15, P less than 0.025). RI of TfC1C2 was 2.3. It suggests that Tfc2 may relate to SLE in this area.

Adult↗
PubMed1991

Enteric neural modulation of slow-wave activity in cat colon.

These studies test the hypothesis that the generation of colonic slow waves can be modulated by stimulation of intrinsic enteric nerves and attempt to identify a neurotransmitter that may be responsible for this change in slow-wave activity. Isolated segments from the mid-colon of the cat generated regular, continuous slow waves at 6.5 +/- 1.1 cpm. Activation of the intrinsic nerves by electrical field stimulation transiently reduced the rate of slow-wave generation to 4.7 +/- 0.7 cpm (P less than 0.001). The response to electrical stimulation was blocked by tetrodotoxin and alpha-chymotrypsin. The following antagonists were not effective in blocking the response: atropine, hexamethonium, phenoxybenzamine, propranolol, methysergide, naloxone, or imidazole. Vasoactive intestinal polypeptide (5 x 10(-7) M) decreased slow wave frequency to 4.5 +/- 0.4 cpm. Vasoactive intestinal polypeptide (VIP) fragment 10-28 inhibited the effect of electrical field stimulation but also decreased the slow-wave frequency. VIP-immunoreactive nerves were much more abundant in the plexus submucosus extremus than in the circular muscle of the muscularis externa. Thus, pacemakers for colonic slow waves may be modulated by intrinsic colonic nerves, and vasoactive intestinal polypeptide may be the neurotransmitter responsible for this modulation.

Animals↗
PubMed1991

Nitric oxide: mediator of nonadrenergic noncholinergic responses of opossum esophageal muscle.

Nonadrenergic noncholinergic (NANC) nerves of the opossum esophagus mediate relaxation of circular muscle from the lower esophageal sphincter (LES) and the off contraction of circular esophageal muscle. The latencies between the end of the stimulus and the off contraction describe a gradient so that the latency is longest in muscle from the caudad esophagus. NG-nitro-L-arginine (L-NNA), an inhibitor of nitric oxide (NO) synthase, and NO were used to test the hypothesis whether NO is a mediator of these nerve-induced responses. Both electrical field stimulation (EFS) of intrinsic esophageal nerves and exogenous NO relaxed LES muscle. Only EFS-induced relaxation was inhibited by L-NNA [half-maximal response (EC50) = 60.0 +/- 20.0 microM]. L-Arginine, the substrate for NO synthase, reversed the inhibitory effect of L-NNA. Exogenous NO did not contact circular esophageal muscle. Both the amplitude (EC50 = 14.7 +/- 4.0 microM) and the latency of the off contraction (EC50 = 41.1 +/- 5.6 microM) were diminished by L-NNA. L-Arginine prevented the action of L-NNA. NG-nitro-L-arginine also attenuated the gradient in the latency of the off response by shortening latencies in muscle from the caudad esophagus. It had no effect on cholinergic nerve-induced contraction of longitudinal esophageal muscle. These data support the hypothesis that NO or an NO-containing compound may be a mediator of NANC nerve-induced responses of the esophagus and LES.

Animals↗
PubMed1991

Nitric oxide: mediator of NANC hyperpolarization of opossum esophageal smooth muscle.

Activation of intrinsic nonadrenergic noncholinergic (NANC) esophageal nerves during peristalsis or by electrical field stimulation (EFS) in vitro produces a hyperpolarization followed by a depolarization of the circular smooth muscle of the opossum esophagus. N omega-nitro-L-arginine (L-NNA), an inhibitor of nitric oxide synthase, and nitric oxide (NO) were used to test the hypothesis that NO or a NO-containing compound is a mediator of this NANC nerve-induced hyperpolarization of circular esophageal smooth muscle. The transmembrane potential difference of esophageal circular smooth muscle cells was recorded with glass microelectrodes. Nerve-mediated membrane responses were evoked by single electrical pulses of 0.5 ms duration and 50 V amplitude. L-NNA abolished the initial hyperpolarization and reduced the amplitude of and the time to maximal depolarization. L-Arginine (1 mM), the substrate for NO synthase, antagonized the effect of L-NNA. Exogenous NO produced hyperpolarization of the smooth muscle membrane potential and attenuated the amplitudes of EFS-induced hyperpolarization and depolarization. The effect of NO was blocked neither by L-NNA nor by tetrodotoxin (1 microM). The data support the hypothesis that NO or a NO-containing compound mediates NANC nerve-induced responses of the esophageal smooth muscle membrane.

Amino Acid Oxidoreductases↗
PubMed1990

Pathways of slow-wave propagation in proximal colon of cats.

Colonic slow waves (SWs) are generated by nonneuronal cells located at the interface of the submucosa and muscularis propria. It has been proposed that SWs arise from a complex of nerves, interstitial cells of Cajal, and smooth muscle found at this location. These experiments test the hypothesis that the propagation of colonic SWs depends on an intact interface between the submucosa and muscularis propria. The electromyogram was recorded from segments of the proximal colon of the cat. All intact tissues generated SWs that propagated in the long and circumferential axes of the colon. Tetrodotoxin did not disrupt SW propagation in either axis. Transection of tissues between recording sites interrupted the spread of SWs in both axes. Transection of the submucosa disrupted the longitudinal spread of SWs, whereas transection of the muscularis propria did not. Removing the submucosa from the midportion of tissue segments oriented in the long axis of the colon resulted in a loss of SWs from the segment devoid of submucosa. Transection of the submucosa of tissue segments oriented in the circular axis of the colon did not disrupt circumferential propagation of SWs. Dissecting a 1-cm-wide segment of submucosa from the midportion of such a circularly oriented tissue did not disrupt the circumferential spread of SWs, and SWs were recorded from the muscle segment that was devoid of submucosa. SWs were not recorded from the segment devoid of submucosa when it was isolated from adjacent intact segments. The data support the hypothesis that the regeneration of SWs during their longitudinal propagation takes place at the interface between the submucosa and muscularis propria.

Animals↗