[Determination of modulus of elasticity of human periodontal membrane]

The modulus of elasticity of periodontal membrane, as an essential parameter indicating the mechanical character of periodontal membrane, is very important in biomechanical studies (e.g. finite element stress analysis and photoelastic analysis) of dental restoration. However, determination of modulus of elasticity of human periodontal membrane has not been reported in China, and there are differences among the foreign reports. In this study, 135 periodontal samples were collected from fresh teeth and alveoli of 6 healthy adults. Drawing and compressing test were performed. The results showed that the tensile modulus of elasticity of human periodontal membrane is between 3.35 and 4.59MPa and the compress modulus of elasticity 0.5402(+/- 0.348) MPa.

Modular structural elements in the replication origin region of Tetrahymena rDNA

Computer analyses of the DNA replication origin region in the amplified rRNA genes of Tetrahymena thermophila identified a potential initiation zone in the 5'NTS [Dobbs, Shaiu and Benbow (1994), Nucleic Acids Res. 22, 2479-2489]. This region consists of a putative DNA unwinding element (DUE) aligned with predicted bent DNA segments, nuclear matrix or scaffold associated region (MAR/SAR) consensus sequences, and other common modular sequence elements previously shown to be clustered in eukaryotic chromosomal origin regions. In this study, two mung bean nuclease-hypersensitive sites in super-coiled plasmid DNA were localized within the major DUE-like element predicted by thermodynamic analyses. Three restriction fragments of the 5'NTS region predicted to contain bent DNA segments exhibited anomalous migration characteristic of bent DNA during electrophoresis on polyacrylamide gels. Restriction fragments containing the 5'NTS region bound Tetrahymena nuclear matrices in an in vitro binding assay, consistent with an association of the replication origin region with the nuclear matrix in vivo. The direct demonstration in a protozoan origin region of elements previously identified in Drosophila, chick and mammalian origin regions suggests that clusters of modular structural elements may be a conserved feature of eukaryotic chromosomal origins of replication.

Mimosine differentially inhibits DNA replication and cell cycle progression in somatic cells compared to embryonic cells of Xenopus laevis

The plant amino acid mimosine has been reported to block cell cycle progression and DNA replication in cultured mammalian cells, perhaps by blocking initiation. In this study, we show that mimosine does not block initiation or any other step in DNA replication in embryonic cells of Xenopus laevis. Mimosine does not block DNA replication in cell-free "cycling" extracts of Xenopus eggs, nor does it block M to S phase transition in cell-free egg extracts released from metaphase arrest. Microinjection of mimosine into 4-cell embryos had no visible effect on development during the first 3 days after fertilization. Prior to the midblastula transition, when the cell cycle consists of alternating S and M phases, neither chromosomal DNA replication nor replication of microinjected plasmid DNA were inhibited by mimosine microinjected into cleaving Xenopus embryos. Microinjection of mimosine after the midblastula transition, when large endogenous stockpiles of DNA replication components have begun to be depleted and Xenopus embryonic cells have acquired G1 and G2 phases, still did not inhibit cell cycle progression or DNA replication. In marked contrast, mimosine arrested the growth of proliferating cultured Xenopus kidney epithelial A6 cells near the G1/S boundary. We conclude that mimosine appears to block DNA replication and cell cycle progression in somatic cells, but has no apparent effect in rapidly dividing Xenopus embryonic cells.

[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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

Genomic organization of the human retinoblastoma gene

Sequence analysis of the human retinoblastoma gene cDNA revealed the presence of repeated elements in the form of direct repeats, inverted repeats and dyad symmetries. The clustering of the dyad symmetrical elements in some exons, #16 and #17, coincides with the hot spots for structural aberrations of the RB-1 locus previously observed in tumors. The RB-1 gene is divided into at least 27 exons distributed over 200 kbp. Three potential Sp1 binding sites are presented within 600 bp upstream of the translation start site. A DNA fragment containing these Sp1 sites ligated to a promotorless CAT gene can promote its transcription in transfected cell culture.

Occupational exposure to benzene in China

Of a total of 528,729 workers exposed to benzene or benzene mixtures in China, 508,818 (96.23%) were examined. Altogether 2,676 cases of benzene poisoning were found, a prevalence of 0.15%. A higher prevalence of benzene poisoning was found in the cities of Hangjou, Hefei, Nanjing, Shenyang, and Xian. The geometric mean concentration of benzene in 50,255 workplaces was 18.1 mg/m3 but 64.6% of the workplaces had less than 40 mg/m3. There was a positive correlation between the prevalence of benzene poisoning and the concentration in shoemaking factories. The prevalence of benzene induced aplastic anaemia in shoemakers was about 5.8 times that occurring in the general population. The results of this investigation show the need for a practicable hygiene standard to prevent benzene poisoning.

Spinal cord influences on the colonic myoelectrical activity of fed and fasted rats

1. The myoelectrical activity of the large intestine of fed and fasted rats was recorded with chronically implanted nichrome wire electrodes after destruction of the spinal cord, after spinal cord transection, and after spinal anaesthesia. 2. After spinal cord ablation, the cyclical organization of the colonic electrical spiking activity, as well as the gastrocolic reflex and accompanying postprandial enhancement of the cyclical pattern of activity, persisted on the proximal and distal colon. On the transverse colon, however, the spiking activity was considerably increased. This latter effect obliterated the gastrocolic response due to feeding but not the subsequent postprandial enhancement of the cyclical pattern of activity. 3. After spinal cord transection, the level of spiking activity also increased on both the transverse and distal colon, but no major changes in cyclical activity or in postprandial responses were recorded. 4. Spinal anaesthesia produced by intrathecal lidocaine increased the motility of the transverse colon to a level which masked the gastrocolic reflex. 5. These results suggest a prevertebral ganglia and/or a local control mechanism for the cyclical organization of the spiking activity of the colon. The central control mechanisms involve mostly spinal inhibitory influences on the transverse colon and supraspinal inhibitory influences on the distal colon.

Peripheral versus central components of the effects of dermorphin on intestinal motility in the fed rat

The effects of subcutaneous (s.c.), intraperitoneal (i.p.), intrathecal (i.t.) and intracerebroventricular (i.c.v.) injection of dermorphin (DER) on intestinal myoelectrical activity were examined in fed rats with chronically implanted electrodes on the small and large bowel. DER s.c. restored the 'fasting' pattern of duodenal activity, i.e., the migrating myoelectric complex (MMC), corresponding to an inhibition by about 40% of the fed pattern for 120 min at a dose as small as 0.5 nM per rat. DER i.p. strongly inhibited (about 65%) the fed pattern for 120 min. A fasting pattern lasting 80 min, or a marked inhibition lasting 150 min were recorded after 0.5 nM DER i.t. or i.c.v., respectively. On the contrary, the colonic pattern of activity was inhibited by DER whatever the route used, although the duration of inhibition was different from each other. For both the small and large intestine, similar doses of DER were more efficient by i.c.v. than by i.t. routes, and by i.p. than by s.c. routes. A plurality of sites of action is suggested, including local receptors which are activated, particularly at the duodenal level by i.p. DER (0.5 nM). The supraspinal component of the immediate effects of i.c.v. DER (0.1 nM) were demonstrated by a preferential effect on the colon that was even more intense than after i.t. DER.

In vivo modulation of intestinal motility and sites of opioid effects in the rat

The effects of subcutaneous (s.c.), intrathecal (i.t.) and intracerebroventricular (i.c.v.) injection of fentanyl and D-Ala2,D-Leu5-enkephalin (DADLE) on intestinal myoelectrical activity were examined in fed rats. In rats with chronically implanted electrodes on the small and large bowel, i.c.v. fentanyl and DADLE restored the 'fasted' pattern of duodenal activity, i.e. the migrating myoelectric complex (MMC) for 8-12 h at a dose as small as 1 nM/kg. In addition, the colonic pattern of activity evaluated as the number of migrating spike bursts (MSB) per min was nearly halved for 1 h following i.c.v. fentanyl (10 nM/kg). Pretreatment with naloxone, but not methylnaloxone prevented these effects on the small and large bowel. Fentanyl (100 nM/kg s.c.) significantly reduced small and large bowel motility, but DADLE (100 nM/kg s.c.) which induced a transient 'fasted pattern' on the duodenum strongly stimulated colonic motor activity. Pretreatment with methylnaloxone prevented the inhibitory effects of s.c. fentanyl but not the colonic excitatory effects of DADLE. The i.t. administration of fentanyl and DADLE did not modify the activity pattern of the bowel. Again, i.t. DADLE stimulated the colon, even after methylnaloxone treatment and at doses 100 times less than the smallest active s.c. dose. The long-lasting changes in small bowel motility and the important delay following DADLE and fentanyl i.c.v., reinforces the hypothesis of a central opioid control of the gastrointestinal motor pattern with possible involvement of released substances.(ABSTRACT TRUNCATED AT 250 WORDS)