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Biomedical subjects

H Cheng

Publications and source records attributed to H Cheng.

At least 145 records · Page 8Linked to original sources
PubMed1999

Effect of hypertonicity on augmentation and potentiation and on corresponding quantal parameters of transmitter release.

Augmentation and (posttetanic) potentiation are two of the four components comprising the enhanced release of transmitter following repetitive nerve stimulation. To examine the quantal basis of these components under isotonic and hypertonic conditions, we recorded miniature endplate potentials (MEPPs) from isolated frog (Rana pipiens) cutaneous pectoris muscles, before and after repetitive nerve stimulation (40 s at 80 Hz). Continuous recordings were made in low Ca2+ high Mg2+ isotonic Ringer solution, in Ringer that was made hypertonic with 100 mM sucrose, and in wash solution. Estimates were obtained of m (no. of quanta released), n (no. of functional release sites), p (mean probability of release), and vars p (spatial variance in p), using a method that employed MEPP counts. Hypertonicity abolished augmentation without affecting potentiation. There were prolonged poststimulation increases in m, n, and p and a marked but transient increase in vars p in the hypertonic solution. All effects were completely reversed with wash. The time constants of decay for potentiation and for vars p were virtually identical. The results are consistent with the notion that augmentation is caused by Ca2+ influx through voltage-gated calcium channels and that potentiation is due to Na+-induced Ca2+ release from mitochondria. The results also demonstrate the utility of this approach for analyzing the dynamics of quantal transmitter release.

Animals↗
PubMed1999

Determinants of DNA sequence specificity of the androgen, progesterone, and glucocorticoid receptors: evidence for differential steroid receptor response elements.

While androgen, progesterone, and glucocorticoid receptors perform distinct physiological functions by regulating unique sets of genes, in vitro they can transactivate a common high-affinity DNA-binding target. Naturally occurring steroid response elements display nucleotide divergence that lowers binding affinity in comparison to the optimal binding element, but enhances receptor-type specificity. We investigated the role of nucleotide deviations within the DNA-binding site for contribution to steroid receptor specificity. We hypothesized that receptor specificity drives the evolution of binding site sequence, rather than strictly receptor-binding affinity. Receptor-selective targets can evolve by some nucleotides selected on the basis of additional bond energy, and others may be selected by differential tolerance to discourage binding from inappropriate receptors. To identify receptor-specific binding sites, we mimicked these dual selection pressures in a receptor-competitive environment in which DNA binding sites for the androgen or progesterone receptors were selected in the presence of the glucocorticoid receptor. These analyses also demonstrated that steroid receptors strongly select nucleotides in the spacer and flanking regions of the half-site and do so in an asymmetric fashion, indicating that steroid receptors interact with DNA in an allosteric manner that affects the transcriptional activation potential.

Amino Acid Sequence↗
PubMed1999

Selective activation of the probasin androgen-responsive region by steroid hormones.

Glucocorticoid and androgen receptors have been shown to function through the same palindromic glucocorticoid response element (GRE) and yet have differential effects on gene transcription. In this study, we examined the functional and structural relationship of the androgen and glucocorticoid receptors with the androgen responsive region (ARR) of the probasin (PB) gene containing two androgen receptor binding sites, ARBS-1 and ARBS-2. Transfection studies indicated that one copy of each cis-acting DNA element was essential for maximal androgen-induced chloramphenicol acetyltransferase (CAT) activity and that androgen selectivity was maintained when multiple copies of the minimal wild type (wt) androgen responsive region containing both ARBS-1 and ARBS-2 (-244 to -96) were subcloned in front of the thymidine kinase promoter. Furthermore, replacing the androgen response region with 1, 2 or 3 copies of either ARBS-1 or ARBS-2 restored less than 4% of the biological activity seen with the wt PB ARR. Multiple copies of either ARBS-1 or ARBS-2 did not result in glucocorticoid-induced CAT gene activity. By comparison, 1 or 2 copies of the tyrosine aminotransferase (TAT) GRE, as well as the mouse mammary tumour virus GRE, were strong inducers of CAT activity in response to both androgen and glucocorticoid treatment. In addition, band shift assays demonstrated that although the synthetic glucocorticoid receptor, GR-DNA binding domain (GR-DBD), and the synthetic androgen receptor, AR2, could interact with the TAT GRE (dissociation constants Kd of 63.9 and 14.1 respectively), only AR2 but not GR-DBD binding could be detected on ARBS-1 and ARBS-2. Our findings provide further evidence that androgen-induced regulation of gene transcription can occur through androgen-specific DNA binding sites that are distinct from the common GRE.

Androgen-Binding Protein↗
PubMed1999

Identification and immunolocalization of chondroitin sulfate proteoglycans in tooth cementum.

Proteoglycans (PGs) display a great diversity in their core proteins as well as carbohydrate structures and are thought to be involved in many biological functions. Recently we have identified and immunolocalized two keratan sulfate PGs, fibromodulin and lumican, in bovine tooth cementum (Cheng et al., Connect. Tissue Res. 34: 87-96, 1996). The objectives of this study were to identify and characterize chondroitin sulfate (CS) PGs in cementum. In order to explore their potential association with mineral, bovine cementum matrix molecules were fractionated into mineral-unbound and -bound matrices by sequential extraction. Both fractions were subjected to DEAE anion exchange column chromatography and the eluate collected was assayed for C4S and C6S isomers by dot blot immunoassay with specific monoclonal antibodies, 2-B-6 and 3-B-3, respectively. Two families of CSPGs were identified mainly in the mineral-unbound fraction. One contained only C4S glycosaminoglycan and the other both C6S and C4S. By biochemical and immunochemical analyses, decorin and biglycan were identified in the former and versican in the latter. The ratio of C6S to C4S isomers of cementum versican was approximately 7:1. Furthermore, these PGs were immunolocalized in and around tooth cementum using antibodies generated against the respective core proteins. Intensive immunostaining for versican was found almost exclusively in the lacunae housing cementocytes in cementum and osteocytes in alveolar bone, respectively. Immunostaining for decorin was mainly associated with collagen fibers in the periodontal ligament and slightly in cementum matrix, while the one for biglycan was mainly in cementoblasts/precementum. These differential tissue distributions of the CSPGs suggest that they may play distinct roles in cementogenesis.

Animals↗
PubMed1999

Detection of mammosomatotrophs in paraffin-embedded specimens of various pituitary adenomas.

BACKGROUND: There are various classification systems for pituitary adenomas based on whether mammosomatotroph cells, which simultaneously express both prolactin (PRL) and growth hormone (GH), can be found. Until the present, the identification of such cells required special techniques and could not be performed in paraffin-embedded specimens. This hindered large-scale studies for detection of mammosomatotrophs in various pituitary adenomas and, as a result, such classification has remained controversial. To establish a methodology for the detection of mammosomatotrophs in paraffin-embedded specimens and to propose a more logical classification for pituitary adenomas, the authors conducted this retrospective study. METHODS: We performed double immunofluorescence staining of PRL and GH in paraffin-embedded specimens of various pituitary adenomas with subsequent observation with a confocal laser-scanning microscope. RESULTS: Mammosomatotrophs were found in four of the 10 GH-secreting adenomas and one of the 10 clinically nonfunctioning adenomas. However, mammosomatotrophs were not identified in all 10 cases of prolactinoma. CONCLUSIONS: This is the first report in the literature that successfully demonstrates the presence of mammosomatotrophs in routine paraffin-embedded pituitary adenomas. The new methodology is important for future study of the function and role of these cells. A large-scale study for mammosomatotrophs in various pituitary adenomas with this method and a more logical classification of pituitary adenomas are proposed.

Adenoma↗
PubMed1999

[Experimental study and preliminary clinical application of bacterial collagenase in catabolizing scars].

OBJECTIVE: To investigate the mechanism of collagenase in degradation of hypertrophic scars and observe the clinical effects of this therapy. METHODS: Both animal experiment and clinical trial were conducted. RESULTS: The injection of collagenase into the hypertrophic scar tissues in nude mice resulted in 86% volume reduction after two injections within two weeks, while the control tissues reduced only by 35% during the same time. Clinically, 13 cases were treated with intralesional injection of bacterial collagenase. The volume reduction rate was 46.92% in average within two weeks. The volume reduction in 4 of 13 cases was above 50%. Three to sixteen months' follow-up of five patients revealed that only one case of keloid recurred after treatment in the second month. Examinations of histological sections and TEM showed the dissolved collagen fiber clearly. CONCLUSION: Collagenase can degrade collagen fiber directly. The prompt significant effects and the mild complications make it a prospective therapy.

Adolescent↗
PubMed1999

[Relationship of polymorphism of LMP2 gene to insulin-dependent diabetes mellitus and DR3 gene].

OBJECTIVE: To investigate the relationship of polymorphism of large multifunctional protease (LMP) 2 genes to insulin-dependent diabetes mellitus (IDDM) and DR3 gene. METHODS: The polymorphism of LMP2 genes was identified by polymerase chain reaction-restriction fragment length polymorphism (PCR-RFLP) in 68 IDDM patients and 71 healthy controls. IDDM patients and healthy controls were respectively divided into 2 groups according to DR3 genotyping. One group included subjects with DR3 gene, and another group subjects without DR3 gene. RESULTS: In the subjects with DR3 gene, the frequencies of LMP2-R/H, LMP2-R/R, LMP2-H/H were 47%, 47% and 6% in the IDDM patients, 13%, 87%, 0% in the controls. Compared with the Controls, the IDDM patients had a higher frequency of LMP2-R/H (P < 0.05) and a lower frequency of LMP2-R/R (P < 0.05). In the subjects without DR3 gene, the frequencies of LMP2-R/H, LMP2-R/R, LMP2-H/H were 58%, 39%, 2.8% respectively in the IDDM patients, and 32%, 54%, 14% respectively in the controls. Compared with the controls, the IDDM patients had a higher frequency of LMP2-R/H (P < 0.05), the frequency of LMP2-R/R in the IDDM patients did not have a significant difference from that in the controls (P > 0.05). CONCLUSIONS: There may be a significant association of LMP2-R/H and LMP2-R/R with the susceptibility to IDDM. The LMP2-R/H is a susceptible gene. The people with LMP2-R/H have a higher risk of suffering from IDDM. The LMP2-R/R is a protective gene. The people with LMP2-R/R have a decreased risk of suffering from IDDM. The effects of LMP2 on ID-DM are not affected by DR3 gene.

Cysteine Endopeptidases↗
PubMed1999

[Inquiring the causes of recurrence of hepatocellular carcinoma after surgical resection].

OBJECTIVE: To analyze the causes of recurrence of hepatocellular carcinoma (HCC) after resection according to pathologic findings of the resected primary tumor and angiographic features of the recurrent tumor. METHODS: In this series, 142 cases with recurrent HCC were analyzed with respect to (1) size, number, gross and histologic findings of the primary tumor, (2) time when recurrence occurred, (3) size, number, blood supply, staining property of, and deposition of lipiodol oil in the recurrent tumor. Following angiography, arterial embolization was performed. RESULTS: In 101 of the 142(71.1%) cases, the primary tumor was > 5 cm in diameter, and in 41 cases (28.9%) it was < 5 cm. In 67.7% of the cases, the capsule of the primary tumor was incomplete or absent. In 47 cases (33.1%), satellite tumor nodules were seen during operation but they were seen on pathologic sections in 94 cases (66.2%). Tumor thrombus was present in the portal vein in 26 (18.3%) and 121 cases (85.2%) during operation and on pathologic examination, respectively. In the majority of the cases (99/142), recurrence occurred within 6 months after operation. The recurrent foci consisted of multiple tumor nodules of < 5 cm in 68.3% of the cases. On angiography, the recurrent tumors were rich in blood supply with good deposition of lipiodol. CONCLUSION: Recurrence is apt to occur in HCC patients with large (> 5 cm) primary tumor which has incomplete or no capsule, satellite tumor nodules and portal vein tumor thrombus. It is suggested to perform angiography 1-2 months after surgery to detect early recurrence and, if confirmed, the patients can be treated by transcatheter arterial chemo-embolization.

Adult↗
PubMed1999

[A methodological study on the evaluation of insulin resistance in vivo].

OBJECTIVE: To investigate the advantage and disadvantage of several methods often used to evaluate insulin resistance and to attempt to modify the disadvantage. METHODS: Three protocols of minimal model technique (MMT), three protocols of basal state approach and four protocols of oral glucose tolerance test (OGTT) were used respectively to calculate insulin sensitivity index (ISI) in 16 subjects with normal glucose tolerance (NGT) and 13 patients with non-insulin-dependent diabetes mellitus (NIDDM). ISI of classical MMT was regarded as standard; ISI of other protocols were analyzed, assessed and compared with that of classical MMT. RESULTS: Except the ISI expressed by the ratio of fasting serum glucose to insulin concentration (FSG/FIns) and the ratio between area under curve (AUC) of glucose and insulin (AUCg/AUCi) in OGTT, ISI of other protocols was significantly higher in NGT group than in NIDDM group (P < 0.05, ISI relative values were 1 and 0.44 - 0.70 respectively) and had stronger relationships as compared with ISI of classical MMT (r = 0.45 - 0.92, P < 0.05). CONCLUSION: The modifications that reduce the samples to 12 or 10 and shorten the time to 120 min for MMT are feasible. Both the homeostasis model assessment and the basal state method designed by LI Guangwei are very simple; they can roughly evaluate insulin sensitivity. OGTT designed by Cederholm is a relatively simple and precise method of measuring IR. Two protocols of OGTT designed by the authors may be accurate methods for evaluating IR. Both FSG/FIns and AUCg/AUCi can not reliably evaluate insulin sensitivity.

Adult↗
PubMed1999

[An experimental method for measuing flexor pulley's mechanical effects by imitating hand in vivo].

Flexor pulley system has an important mechanical effect on digital flexion function. An experimental method was designed to measure the pulleys' mechanical effects by using hand in vitro to imitate hands in vivo. The pulleys' function was evaluated by pulley incision and pulley preservation, and percentage loss of work was used as an index. The results demonstrate that this experiment is reasonable in design and methodology.

Adult↗
PubMed1999

[Effects of immobilization on the mechanical properties of rabbit patellar tendon].

The aim of this study was to evaluate the effect of immobilization on the mechanical properties of rabbit patellar tendon(PT). IN this study, the rabbit knee was immobilized in extension for 6 weeks, then the mechanical properteis of PT were investigated. The results showed that the stress-strain relationship of PT could be expressed with exponential functions, and there were significant differeces between the normal group and the immobilized group in their theoretical curves of stress-strain relationship and two material constants of PT. Also, significant differences were found in tensile strength and tangent modulus between the two groups, but the maximum load of PT in the immobilized group did not decrease significantly. On the basis of the findings listed above, it is believed that PT would remodel and change its mechanical properties in response to the changes of mechanical stress exerted on it when the knee is immobilized.

Animals↗
PubMed1998

Termination of Ca2+ release by a local inactivation of ryanodine receptors in cardiac myocytes.

In heart, a robust regulatory mechanism is required to counteract the regenerative Ca2+-induced Ca2+ release from the sarcoplasmic reticulum. Several mechanisms, including inactivation, adaptation, and stochastic closing of ryanodine receptors (RyRs) have been proposed, but no conclusive evidence has yet been provided. We probed the termination process of Ca2+ release by using a technique of imaging local Ca2+ release, or "Ca2+ spikes", at subcellular sites; and we tracked the kinetics of Ca2+ release triggered by L-type Ca2+ channels. At 0 mV, Ca2+ release occurred and terminated within 40 ms after the onset of clamp pulses (0 mV). Increasing the open-duration and promoting the reopenings of Ca2+ channels with the Ca2+ channel agonist, FPL64176, did not prolong or trigger secondary Ca2+ spikes, even though two-thirds of the sarcoplasmic reticulum Ca2+ remained available for release. Latency of Ca2+ spikes coincided with the first openings but not with the reopenings of L-type Ca2+ channels. After an initial maximal release, even a multi-fold increase in unitary Ca2+ current induced by a hyperpolarization to -120 mV failed to trigger additional release, indicating absolute refractoriness of RyRs. When the release was submaximal (e.g., at +30 mV), tail currents did activate additional Ca2+ spikes; confocal images revealed that they originated from RyRs unfired during depolarization. These results indicate that Ca2+ release is terminated primarily by a highly localized, use-dependent inactivation of RyRs but not by the stochastic closing or adaptation of RyRs in intact ventricular myocytes.

Animals↗
PubMed1998

Direct measurement of SR release flux by tracking 'Ca2+ spikes' in rat cardiac myocytes.

1. Ca2+ release flux across the sarcoplasmic reticulum (SR) during cardiac excitation-contraction coupling was investigated using a novel fluorescence method. Under whole-cell voltage-clamp conditions, rat ventricular myocytes were dialysed with a high concentration of EGTA (4.0 mM, 150 nM free Ca2+), to minimize the residence time of released Ca2+ in the cytoplasm, and a low-affinity, fast Ca2+ indicator, Oregon Green 488 BAPTA-5N (OG-5N; 1.0 mM, Kd approximately 31 microM), to optimize the detection of localized high [Ca2+] in release site microdomains. Confocal microscopy was employed to resolve intracellular [Ca2+] at high spatial and temporal resolution. 2. Analytical and numerical analyses indicated that, under conditions of high EGTA concentration, the free [Ca2+] change is the sum of two terms: one major term proportional to the SR release flux/Ca2+ influx, and the other reflecting the running integral of the released Ca2+. 3. Indeed, the OG-5N transients in EGTA-containing cells consisted of a prominent spike followed by a small pedestal. The OG-5N spike closely resembled the first derivative (d[Ca2+]/dt) of the conventional Ca2+ transient (with no EGTA), and mimicked the model-derived SR Ca2+ release function reported previously. In SR Ca2+-depleted cells, the OG-5N transient also closely followed the waveform of L-type Ca2+ current (ICa). Using ICa as a known source of Ca2+ influx, SR flux can be calibrated in vivo by a linear extrapolation of the ICa-elicited OG-5N signal. 4. The OG-5N image signal was localized to discrete release sites at the Z-line level of sarcomeres, indicating that the local OG-5N spike arises from 'Ca2+ spikes' at transverse (T) tubule-SR junctions (due to the imbalance between calcium ions entering the cytosol and the buffer molecules). 5. Both peak SR release flux and total amount of released Ca2+ exhibited a bell-shaped voltage dependence. The temporal pattern of SR release also varied with membrane voltage: Ca2+ release was most synchronized and produced maximal peak release flux (4.2 mM s-1) at 0 mV; in contrast, maximal total release occurred at -20 mV (71 versus 61 microM at 0 mV), but the localized release signals were partially asynchronous. Since the maximal conventional [Ca2+] transient and contraction were elicited at 0 mV, it appears that not only the amount of Ca2+ released, but also the synchronization among release sites affects the whole-cell Ca2+ transient and the Ca2+-myofilament interaction.

Algorithms↗
PubMed1998

Transcription factor MSY-1 regulates expression of the murine growth hormone receptor gene.

Previous studies identified and partially characterized a 42-base pair regulatory element in the 5'-flanking region of the L1 transcript of the murine growth hormone (GH) receptor gene that interacted with both double- and single-stranded DNA-binding proteins. We present evidence that the double-stranded DNA-binding protein is NF-Y, a CCAAT box-binding protein. Experiments with a dominant negative form of NF-Y indicate that NF-Y does not play a direct role in regulating the activity of the FP42 element. A cDNA clone that specifically interacts with the upper (coding) strand of the regulatory element was isolated by screening a cDNA expression library using the Southwestern technique. DNA sequencing, electrophoretic mobility shift assay, Southwestern blot analysis, and supershift EMSA confirm the identity of the single-stranded binding protein to be MSY-1, a DNA-binding protein that is evolutionary conserved from prokaryotes to eukaryotes. Mapping of single-stranded DNA configurations reveals that MSY-1 can facilitate the formation of single-stranded DNA regions in the GH receptor 5'-flanking region. Transient transfection experiments support the role of MSY-1 as a repressor of GH receptor gene activation. Southwestern blot analysis indicates that the levels of nuclear MSY-1 are decreased in the livers of pregnant mice, suggesting a role for MSY-1 in the increased expression of the GH receptor during pregnancy.

Animals↗
PubMed1998

An electrochemical, kinetic, and spectroscopic characterization of [2Fe-2S] vegetative and heterocyst ferredoxins from Anabaena 7120 with mutations in the cluster binding loop.

Residues within the cluster binding loops of plant-type [2Fe-2S] ferredoxins are highly conserved and serve to structurally stabilize this unique region of the protein. We have investigated the influence of these residues on the thermodynamic reduction potentials and rate constants of electron transfer to ferredoxin:NADP+ reductase (FNR) by characterizing various single and multiple site-specific mutants of both the vegetative (VFd) and the heterocyst (HFd) [2Fe-2S] ferredoxins from Anabaena. Incorporation of residues from one isoform into the polypeptide backbone of the other created hybrid mutants whose reduction potentials either were not significantly altered or were shifted, but did not reconcile the 33-mV potential difference between VFd and HFd. The reduction potential of VFd appears relatively insensitive to mutations in the binding loop, excepting nonconservative variations at position 78 (T78A/I) which resulted in approximately 40- to 50-mV positive shifts compared to wild type. These perturbations may be linked to the role of the T78 side chain in stabilizing an ordered water channel between the iron-sulfur cluster and the surface of the wild-type protein. While no thermodynamic barrier to electron transfer to FNR is created by these potential shifts, the electron-transfer reactivities of mutants T78A/I (as well as T48A which has a wild-type-like potential) are reduced to approximately 55-75% that of wild type. These studies suggest that residues 48 and 78 are involved in the pathway of electron transfer between VFd and FNR and/or that mutations at these positions induce a unique, but unproductive orientation of the two proteins within the protein-protein complex.

Anabaena↗
PubMed1998

Evolution of the avian sex chromosomes from an ancestral pair of autosomes.

Among the mechanisms whereby sex is determined in animals, chromosomal sex determination is found in a wide variety of distant taxa. The widespread but not ubiquitous occurrence, not even within lineages, of chromosomal sex determination suggests that sex chromosomes have evolved independently several times during animal radiation, but firm evidence for this is lacking. The most favored model for this process is gradual differentiation of ancestral pairs of autosomes. As known for mammals, sex chromosomes may have a very ancient origin, and it has even been speculated that the sex chromosomes of mammals and birds would share a common chromosomal ancestry. In this study we showed that the two genes, ATP5A1 and CHD1, so far assigned to the female-specific W chromosome of birds both exist in a very closely related copy on the Z chromosome but are not pseudoautosomal. This indicates a common ancestry of the two sex chromosomes, consistent with the evolution from a pair of autosomes. Comparative mapping demonstrates, however, that ATP5A1 and CHD1 are not sex-linked among eutherian mammals; this is also not the case for the majority of other genes so far assigned to the avian Z chromosome. Our results suggest that the evolution of sex chromosomes has occurred independently in mammals and birds.

Animals↗
PubMed1998

Deep-Sea coral evidence for rapid change in ventilation of the deep north atlantic 15,400 years Ago

Coupled radiocarbon and thorium-230 dates from benthic coral species reveal that the ventilation rate of the North Atlantic upper deep water varied greatly during the last deglaciation. Radiocarbon ages in several corals of the same age, 15.41 +/- 0.17 thousand years, and nearly the same depth, 1800 meters, in the western North Atlantic Ocean increased by as much as 670 years during the 30- to 160-year life spans of the samples. Cadmium/calcium ratios in one coral imply that the nutrient content of these deep waters also increased. Our data show that the deep ocean changed on decadal-centennial time scales during rapid changes in the surface ocean and the atmosphere.

Journal Article↗