Biomedical subjects

S B Cheng-Chew

Publications and source records attributed to S B Cheng-Chew.

16 recordsLinked to original sources

PubMed2001

Expression of cystic fibrosis transmembrane conductance regulator in rat efferent duct epithelium.

The expression of cystic fibrosis transmembrane conductance regulator (CFTR) was studied in rat efferent ducts. Under whole-cell patch-clamp condition, efferent duct cells responded to intracellular cAMP with a rise in inward current. The cAMP-activated current exhibited a linear I-V relationship and time- and voltage-independent characteristics. The current was inhibited by the Cl(-) channel blocker diphenylamine 2,2'-dicarboxylic acid (DPC) in a voltage-dependent manner and reversed at 24 +/- 0.5 mV, close to the equilibrium potential for Cl(-) (30 mV), suggesting that the current was Cl(-) selective. The cAMP-activated current displayed a permeability sequence of Br(-) > Cl(-) > I(-). Short-circuit current measurement in cultured rat efferent duct epithelia also revealed a cAMP-activated inward current inhibitable by DPC. These electrophysiological properties of the cAMP-activated Cl(-) conductance in the efferent duct were consistent with those reported for CFTR. In support of the functional studies, reverse transcription polymerase chain reaction revealed the presence of CFTR message in cultured efferent duct epithelium. Immunohistochemical studies in intact rats also demonstrated CFTR protein at the apical membrane of the principal cells of efferent duct. CFTR may play a role in modulating fluid transport in the efferent duct.

Animals↗

PubMed2001

Nongenomic effect of testosterone on chloride secretion in cultured rat efferent duct epithelia.

Short-circuit current (I(sc)) technique was used to investigate the role of testosterone in the regulation of chloride secretion in cultured rat efferent duct epithelia. Among the steroids tested, only testosterone, and to a lesser extent, 5alpha-dihydrotestosterone (5alpha-DHT), reduced the basal and forskolin-induced I(sc) in cultured rat efferent duct epithelia when added to the apical bathing solution. Indomethacin, a 3alpha-hydroxysteroid dehydrogenase, did not affect the inhibitory effect of 5alpha-DHT. The effect of testosterone occurred within 10-20 s upon application and was dose dependent with apparent IC(50) value of 1 microM. The effect was abolished by removal of Cl(-) but not HCO from the normal Krebs-Henseleit solution, suggesting that testosterone mainly inhibited Cl(-) secretion. The efferent duct was found to be most sensitive to testosterone, while the caput and the cauda epididymidis were only mildly sensitive. Cyproterone acetate, a steroidal antiandrogen, or flutamide, a nonsteroidal antiandrogen, did not block the effect of testosterone on the forskolin-induced I(sc), nor did protein synthesis inhibitors, cycloheximide, or actinomycin D. However, pertussis toxin, a G(i) protein inhibitor, attenuated the inhibition of forskolin-induced I(sc) by testosterone. Testosterone caused a dose-dependent inhibition of forskolin-induced rise in cAMP in efferent duct cells. It is suggested that the rapid effect of testosterone was mediated through a membrane receptor that is negatively coupled to adenylate cyclase via G(i) protein. The role of nongenomic action of testosterone in the regulation of electrolyte and fluid transport in the efferent duct is discussed.

1-Methyl-3-isobutylxanthine↗

PubMed1996

Localisation of VIP-and CGRP-like substances in the skin and sinus hair follicles of various mammalian species.

Using an ultrastructural postembedding immunogold technique, we demonstrated vasoactive intestinal polypeptide (VIP)- and calcitonin gene-related peptide (CGRP)-like immunoreactivity in the Merkel cell dense-cored granules of skin and sinus hair follicles of adult cat and dog. The VIP-like substance was located in cat Merkel cells while both VIP- and CGRP-like substances were colocalised in dog Merkel cells. In cat Merkel cells, the magnitude of labelling of VIP was qualitatively higher than in dog Merkel cells. In the dog Merkel cell, CGRP appeared as the most abundant peptide. Dense-cored granules were labelled for these peptides. In addition, mast cells encountered in the dermal region of dog skin were also found to be immunolabelled by VIP antiserum. The immunoreaction was found to be confined to the secretory granules of the cells. Furthermore, all non-myelinated nerve plexuses encountered in the dermal region of the skin and the sinus hair follicles of the various mammalian species studied were immunolabelled by CGRP antiserum. The specific location was again restricted to the dense-cored granules present in these nerves. As VIP and CGRP have potent vasodilatory effects, our observations suggest that Merkel cells may play a separate or synergistic role in regulatory functions of the skin neuroendocrine cell, exerting their influence by paracrine, endocrine and neurocrine pathways, or a combination of these. Different methodologies of double labelling with different sizes of gold particles are also discussed.

Animals↗

PubMed1992

The role of calcitonin gene-related peptide in the regulation of anion secretion by the rat and human epididymis.

A study was carried out to investigate the role of the calcitonin gene-related peptide (CGRP) in the regulation of electrolyte transport in the rat and human epididymis. In monolayer cultures derived from the rat cauda epididymal cells, CGRP stimulated the short-circuit current (SCC) in a dose-dependent manner with the EC50 (concentration required to produce 50% of the response) at 15 nmol/l. This effect of CGRP was seen when the peptide was added to the basolateral aspect of the cells; apical addition having negligible effect. The CGRP-induced rise in the SCC was dependent on the presence of chloride in the bathing solution. Calcitonin had no effect on the SCC and did not affect the CGRP-induced rise in the SCC. The effect of CGRP on secretion was inhibited in a competitive fashion by the CGRP receptor antagonist CGRP(8-37). In contrast to bradykinin, angiotensin II and endothelin I, the effect of CGRP was independent of prostaglandin synthesis. Measurement of intracellular adenosine 3':5'-cyclic monophosphate showed a time- and dose-dependent increase upon stimulation with CGRP. CGRP also stimulated the SCC in monolayers grown from the human epididymis. The current could be inhibited by apical application of the chloride channel blocker, diphenylamine-2-carboxylate. Immunoreactive CGRP was found in the epithelia of rat and human cauda epididymidis. It is suggested that CGRP may regulate the electrolyte and fluid secretion in the epididymis, thereby providing an optimal microenvironment for the maturation and storage of spermatozoa.

Aged↗

PubMed1991

Functional study and immunocytochemical identification of endothelin in cultured epididymal cells and intact epididymis of the rat.

Endothelin, a novel potent vasoconstrictor peptide produced by vascular endothelial cells, stimulated anion secretion by a cultured secretory epithelium derived from the rat epididymis as measured by changes in short-circuit current (SCC). Stimulation of the SCC was observed when endothelin was added to the basolateral or the apical side of the epithelium. The response to basolateral application was greater than that to apical application. The EC50 values were found to be 1.3 and 3.0 nM for basolateral and apical application, respectively. These values were about one-half to one order of magnitude higher than that required for its vasoconstrictor action. The stimulation of SCC by endothelin was likely to be due to an increase to anion secretion as removal of Cl from the incubation medium markedly reduced the SCC response to endothelin. Diphenylamine-2-carboxylate (DPC, 0.1 mM), a Cl-channel blocker, added to the apical side also inhibited the endothelin-induced rise in SCC. The stimulation of SCC by endothelin was accompanied by a rise in the intracellular cyclic AMP content in epididymal monolayers. Immunofluorescence staining has shown the presence of immunoreactive endothelin-like compound in the interstitium and epithelial cells of the rat epididymis. It is speculated that endogenous endothelin plays an important role in the control of water and electrolyte transport in the epididymis.

Animals↗

PubMed1986

Responsiveness and ultrastructure of slowly adapting type I cutaneous mechanoreceptors in vitamin A deficient rats.

Single-unit recordings were made from afferent nerve fibres supplying slowly adapting type I (s.a. I) cutaneous mechanoreceptors in anaesthetized vitamin A deficient and control rats. Trains of thirty repetitive mechanical stimuli with 0.1 s rise time, 1.9 s plateau phase, and 0.7 s interstimulus interval were applied. A feed-back mechanism maintained the force of stimulation at 20 mN during the plateau phases and the contact force between stimuli at 0.5 mN. All displacement values in the group of vitamin A deficient rats were significantly larger than the corresponding control values. Residual indentations were increased by 70-100% while maximal indentations were only about 40% higher. These results indicate a non-linear increase in compliance of the skin and underlying tissues. S.a. I receptors were found to be significantly less responsive in vitamin A deficient animals. Mean numbers of impulses were about 25% lower in the vitamin A deficient group than in controls throughout the entire train of thirty stimuli. In vitamin A deficient rats, Merkel cells and adjoining nerve terminals showed signs of degeneration of a variety of cell organelles, particularly the mitochondria. Degenerative changes induced by vitamin A deficiency especially in the Merkel cells appeared to be a major cause of the reduction of responsiveness in s.a. I receptors.

Animals↗

PubMedDate not supplied

Association of EGFR gene fragments with nuclear matrix proteins in high and low metastatic melanoma cell lines.

Two melanoma cell lines with different metastatic potential were used to study the association of EGFR gene fragments with the nuclear matrix and its role in cancer metastasis by polymerase chain reaction. A 940 bp positive amplification by PCR using primers I-II was demonstrated in a high metastatic cell line, WM451. A 110 bp positive amplification was shown using primers III-IV in both high and low metastatic cell lines. This finding demonstrates that EGFR gene fragments are tightly bound to the nuclear matrix and suggests that binding ability of this EGFR gene fragment to nuclear matrix seems to be closely related to metastatic potential in melanoma cell lines WM45 1 and WM35.

Antigens, Nuclear↗

PubMedDate not supplied

Distribution of a novel nuclear protein in normal and regenerating liver cells.

Monoclonal antibodies to a rat liver nuclear protein (B2, 68 kda, pI: 6.5-8.2) have been established and characterized to localize the distribution of this antigen in nuclear organization. It was demonstrated that this nuclear protein B2 is associated with actively transcribed nucleosomes and the nuclear matrix as revealed by immunogold labelling. In the regenerating liver cell, the immunogold particles are predominantly in the euchromatin as compared to the resting liver cells which are mainly in nuclear matrix and heterochromatin. It was also demonstrated that the incorporation of 32P into the nuclear protein B2 is increased 6-fold in the actively transcribed nucleosomes as compared to the nuclear matrix, as analyzed by two-dimensional polyacrylamide gel electrophoresis. We hypothesize that this nuclear protein may act as an anchorage point either for actively transcribed RNA or for DNA replication. Once this protein is highly phosphorylated, it dissociates from the nuclear envelope and can then dynamically interact with active nucleosomes within the nucleus.

Animals↗

PubMedDate not supplied

An immuno-electron microscopic study on the relationship between nuclear matrix and DNA in rat spermatocytes.

The nucleus of the mammalian spermatid undergoes a series of changes in its chromatin and nucleoprotein composition during transport from testis to epididymis. The sperm DNA is very tightly packaged by protamines instead of histones in somatic cells. However, the nuclear matrix and its association with DNA have not yet been definitively scrutinized with the electron microscope. The present study reveals that the protamine-depleted sperm nuclear matrix appears as a network of thick and thin filaments with glodular structures attached the these fibers. Monoclonal antibody to single- and doublestranded DNA was used to localize remnant DNA after extraction. By immunofluorescence microscopy, monoclonal antibody against DNA was localized outside the nucleus as a halo. Immuno-electron microscopy showed that gold particles were mainly associated with nuclear matrix surrounding the sperm head. Our results suggest a specific structural organization of sperm DNA with its matrix.

Animals↗

PubMedDate not supplied

Ultrastructural study on the development of the rat [correction of mouse] spermatocyte nuclear matrix during epididymal maturation.

The rat sperm nucleus, after sequential extraction with detergents, nuclease and ammonium sulfate, consists of a skeletal structure that resembles the original nuclear shape. This chromatin-depleted skeleton is formed by thick and thin fibers as well as globular structures of different sizes. These fibers form anastomosis. The sperm nuclei obtained from testis and caput epididymis exhibits a loose fibrous network with thin fibers at the center. The entire nucleus of the sperm in the caudal epididymis is formed by a dense network of thick and thin fibers. These highly branched matrix fibers had diameters of 35 and 12 nm. It is concluded that the increase in density of the matrix fibers is related to the condensation of the chromatin in the maturation of the spermatozoa.

Animals↗

PubMedDate not supplied

Electron microscopic analysis of the relationship between nuclear matrix stability and cell differentiation.

Two cell lines, the less differentiated CC2/CUHK2 and the more differentiated CC3/CUHKE3, were used to study the difference in nuclear matrix stability against DNase 1 digestion. The nuclear matrix was almost totally extracted when the CC3/CUHK3 cells were digested with 100 micrograms/ml DNase 1, while that of the CC2/CUHK2 cells was still present even when 200 micrograms/ml DNase 1 was used. It is suggested that more differentiated cells have a less stable nuclear matrix while the less differentiated ones have a more stable nuclear matrix. The same phenomenon was also observed in normal human and rat cervical epithelia. The nuclear matrix of the poorly differentiated basal cells was more stable than that of the more differentiated superficial cells. This cell differentiation stage dependent stability of the nuclear matrix is probably related to the nuclear activity and gene expression.

Animals↗

PubMedDate not supplied

Microwave fixation of nuclear matrix in tumor cells.

Microwave irradiation provides good fixation of human and animal tissues for light and electron microscopy. In this study, microwave irradiation was used for the fixation of cytoplasmic and nuclear matrix in tumor cells. The nuclear matrix appears well preserved and exhibits a network formed by thick and thin filaments. Hence microwave fixation can be used as a quick and effective method for the study of the morphology of nuclear matrix.

Animals↗

PubMedDate not supplied

Fine structural observations on the human sperm nuclear matrix.

The nucleus of the mammalian sperm is formed after a series of morphological and biochemical changes during spermatogenesis. The human sperm nucleus, after sequential extraction with detergents, nuclease and ammonium sulfate, consists of a fibroskeletal structure which maintains the original nuclear shape. The chromatin-depleted skeleton is formed by thick and thin fibers as well as electron-dense patches of different sizes. These highly branched matrix fibers had average diameters of 35 and 12 nm. Polarization of the fibroskeletal structure is apparent and can be used as a good model to study the function of nuclear matrix in nuclear compartmentation in germ cells.

Chromatin↗

PubMedDate not supplied

Microwave-enhanced immunohistochemical staining of a formalin-sensitive antigen-laminin receptor.

Many potentially useful antigens have been difficult to detect in formalin-fixed, paraffin-embedded tissues. Recently a number of pathological and research laboratories have demonstrated that some antigens masked by formalin fixation could be restored to detectability by microwave heating. Previously, we were unable to demonstrate laminin receptor in cells processed by the routine fixation. Our results showed that microwave heating together with trypsin produced the best immunohistochemical staining for this receptor. Nevertheless, no significance was found in the levels of 67 kD LR in high and low metastatic tumor cell lines.

Adenocarcinoma↗

PubMedDate not supplied

The association of HPV 16 DNA with specific nuclear matrix proteins of normal and cervical carcinoma cell.

Human papillomavirus type 16 (HPV 16) has been found to be integrated into the DNA of epithelial cells in most cervical cancers. The HPV16 DNA is bound to different nuclear matrix proteins in normal and cervical carcinoma cells. It has high affinity, for acidic proteins in cancer cells. The molecular weights of the acidic proteins are 200 kD, 186 kD and 67 kD. On the other hand, the viral DNA seemed to bind to higher molecular weight basic nuclear matrix proteins (250 kD, 150 kD) of normal cells. Further investigation of the functional roles of these nuclear matrix proteins may provide insight into the process of carcinogenesis of the cervix.

DNA, Viral↗

PubMedDate not supplied

Nuclear matrix of human ovarian cancer cells in vitro.

The epithelial neoplasia constitute 60% of all primary tumors of the ovary and 90% of these are malignant. Nuclear matrix has been found to be involved in normal and abnormal nuclear activities. Previously, we have identified tumor-associated nuclear matrix proteins in cancers of human liver, nasopharynx and cervix. In this study, we compared nuclear matrices of immortalized ovarian and cancer cell lines by morphometric and 2-D gel electrophoresis analysis.

Electrophoresis, Gel, Two-Dimensional↗