Search PubMed⌕ Search

Biomedical subjects

D Brown

Publications and source records attributed to D Brown.

At least 667 records · Page 37Linked to original sources
PubMed1992

Localization of ecto-ATPase in rat kidney and isolated renal cortical membrane vesicles.

Brush-border (BBMV) and basolateral membrane vesicles (BLMV) from rat renal cortex exhibit an ecto-ATPase activity that is distinct from other ATPases. We have examined the cellular and regional distribution of this enzyme in rat kidney using antibodies against rat liver ecto-ATPase. In isolated vesicles, the distribution shown by biochemical assays of ATPase activity was confirmed by immunocytochemistry and Western blotting. Indirect immunofluorescence and immunogold labeling showed that brush borders of the S1 and S3 segments of the proximal tubule (PT) were stained, but the S2 segment was negative. Staining was most intense in the S3 segment. The luminal membrane of the initial part of the thin descending limb of Henle also showed a marked staining. Surprisingly, basolateral plasma membranes of PT had no detectable staining. However, the plasma membrane of endothelial cells was heavily stained, both in larger vessels and in peritubular capillaries. Using an antibody against rat thrombomodulin, a marker for endothelial cell plasma membranes, we showed that preparations of BBMV, BLMV, and endocytic vesicles are all contaminated with these membranes. This may explain, at least partially, the biochemically measured ecto-ATPase activity in renal cortical membrane vesicles. Finally, no specific staining in the kidney was found using polyclonal antipeptide antibodies against the "long form" of liver ecto-ATPase, either by immunocytochemistry or by Western blotting. This indicates either that there is no long isoform of the ecto-ATPase in the kidney or that the intracellular domains of the long form are different in the two tissues.

Adenosine Triphosphatases↗
PubMed1992

Colocalization of GAPDH and band 3 (AE1) proteins in rat erythrocytes and kidney intercalated cell membranes.

Glyceraldehyde-3-phosphate dehydrogenase (EC 1.2.2.12) (GAPDH) is a multifunctional protein that associates with the cytoplasmic face of intact human erythrocyte membranes. This association has been postulated to be critically dependent on the interaction of GAPDH with the highly acidic NH2-terminal domain of the principal integral membrane protein of the erythrocyte plasma membrane, the band 3 anion exchanger (AE1). This domain is not conserved in murine erythrocyte AE1 and is fully deleted in the alternatively spliced AE1 isoform that is expressed in the kidney. The lack of conservation of this domain has been proposed to explain the reported absence of GAPDH association with rodent erythrocyte membranes. To determine whether GAPDH could be associated with AE1 proteins in rodent cell membranes, specific rabbit antibodies to peptide sequences of rat GAPDH and mouse AE1 were used to immunolocalize these proteins in sequential semithin sections of rat erythrocytes and kidney medulla. In rat erythrocytes, GAPDH immunoreactivity was predominantly membrane associated and colocalized with AE1. In the kidney medulla, GAPDH was concentrated in the basolateral membrane of type A intercalated cells, where it colocalized with the alternatively spliced kidney form of AE1. GAPDH immunoreactivity was not detected in the plasma membrane of any other cell type in the kidney, indicating its predominant association with AE1-rich membranes. If this membrane interaction occurs via AE1 binding, then GAPDH must have binding sites in addition to those previously described for such binding in human AE1.

Amino Acid Sequence↗
PubMed1992

Expression of mRNA (D2) encoding a protein involved in amino acid transport in S3 proximal tubule.

A rat kidney- and intestine-specific cDNA (D2) that induces high-affinity, Na(+)-independent uptake of cystine and dibasic and neutral amino acids into cRNA-injected Xenopus oocytes was recently isolated by expression cloning in our laboratory (R. G. Wells and M. A. Hediger. Proc. Natl. Acad. Sci. USA 89: 5596-5600, 1992). At present it is not known whether the D2-encoded protein functions as a transporter or as a transporter activator. To gain more insight into the role of D2 in renal amino acid transport, we studied the site of its expression in the kidney. This was determined by Northern blot analysis and by using a combination of in situ hybridization and immunocytochemistry with antibodies that recognize specific proximal tubule segments. D2 antisense RNA hybridized to the same tubular segments that were strongly positive for anti-ecto-adenosinetriphosphatase but negative for carbonic anhydrase type IV and the facilitated glucose transporter GLUT2. We conclude that D2 mRNA is strongly expressed in the rat kidney proximal tubule S3 segment, although there is weak hybridization to the S1 and S2 segments. The signal is absent in all other parts of the kidney. The S3 specific expression of D2 mRNA coincides with the site of high-affinity transport of cystine and other amino acids, consistent with the proposed involvement of D2 in these processes.

Amino Acids↗
PubMed1992

Effect of abdominal compression on diaphragmatic tendon organ activity.

Previous studies suggest that afferents in the diaphragm participate in the reflex reduction in phrenic nerve efferent activation when the length of the diaphragm is increased by abdominal compression. The present study determined the response of tendon organ afferents in the diaphragm to increases in abdominal pressure. Five cats were anesthetized with thiopental sodium (60 mg/kg ip to induce, supplemented intravenously). Extracellular recordings from nine individual tendon organ afferents were made from right cervical dorsal root ganglia 5 and 6. Right crural electromyographic activity was recorded. The right extrathoracic phrenic nerve was isolated and stimulated to identify tendon organs on the basis of conduction velocity and response to twitch. The response to ramp-and-hold stretch of the diaphragm was used as an additional test to differentiate tendon organs from muscle spindles. The mean level of activity of the tendon organs during the 1st s of the inspiratory phase was 47 +/- 10 (SD) Hz. Abdominal compression was associated with a significant increase in the activity of these afferents to 61 +/- 11 Hz. Results indicate that increases in the activity of diaphragmatic tendon organs are associated with moderate increases in abdominal pressure and are likely the result of elevations in the active tension developed by the diaphragm. Combined with results from previous studies, it is possible that diaphragmatic tendon organs may play a role in the attenuation of respiratory muscle activation when abdominal pressure is increased.

Abdomen↗
PubMed1992

Effects of stage of the cycle and estradiol-17 beta on oxytocin synthesis by ovine granulosa and luteal cells.

Individual ovine follicles or corpora lutea (CL) were obtained at different stages of the estrous cycle to compare the pattern of oxytocin synthesis with time in vitro. Granulosa cells from follicles in the early follicular phase produced minimal amounts of oxytocin whereas output from preovulatory (post LH surge) follicles increased to a peak of 540 pg/10(4) cells.24 h on days 4-7 in vitro declining to 180 pg/10(4) cells.24 h by day 11. Production from day 1 CL was also high, peaking at 1639 pg/10(4) cells.24 h. In contrast the capacity for oxytocin synthesis by day 2 CL had already declined, with peak output reaching only 185 pg/10(4) cells.24 h on days 3-4. Day 9 CL produced small amounts of oxytocin (50 pg/10(4) cells in the first 24 h) followed by a low output thereafter. The effect of estradiol-17 beta (E2 beta) on oxytocin synthesis was examined. The results were dependent on the stage of the cycle at which the cells were obtained. Oxytocin production was significantly stimulated in three and inhibited in four out of nine preovulatory follicles by the addition of 50 or 500 ng/ml E2 beta, whereas in days 1 and 2 CL E2 beta consistently inhibited oxytocin synthesis and in day 9 CL no response was found. These data indicate that the ovarian capacity to synthesize oxytocin varies markedly at different stages of the cycle, and that cells obtained close to ovulation do not experience the rapid down-regulation in oxytocin synthesis which occurs in vivo in the early luteal phase. E2 beta may switch from having a stimulatory to an inhibitory action on oxytocin synthesis shortly before ovulation.

Animals↗
PubMed1992

Disruption of synchrony between parasite growth and host cell division is a determinant of differentiation to the merozoite in Theileria annulata.

The multinucleated macroschizont stage of the protozoon Theileria annulata is an intracellular parasite of bovine leukocytes. The parasite induces the host cell to proliferate, and divides in synchrony with the immortalised host cell. Differentiation to the next stage occurs within the host cell culminating in the release of merozoites and destruction of the leukocyte. In this study clones of Theileria annulata macroschizont-infected cell lines were isolated by limiting dilution and tested for differentiation to the merozoite stage (merogony). Two cloned cell lines underwent differentiation with enhanced efficiency, while two others were of lower efficiency. Quantification was carried out using monoclonal antibodies, which showed that over 90% of the cells in an enhanced cloned cell line could be induced to differentiate. By carrying out induction at 41 degrees C for limited periods of time followed by culture at 37 degrees C evidence was obtained that differentiation to the merozoite is a two-step process: a preliminary reversible phase, followed by a second irreversible phase of differentiation. Analysis of the nuclear number of the macroschizont and the growth rate of the cloned cell lines showed that the ability to differentiate was associated with an increase in nuclear number (size) of the macroschizont, generated by a disruption in the synchrony between parasite growth and host cell division. We believe that these results reveal a relationship between a reduction in parasite division and differentiation, and that there are similarities between stage differentiation in parasites and cellular differentiation in higher eukaryotes.

Animals↗
PubMed1992

Polarized targeting of V-ATPase in kidney epithelial cells.

The membrane-associated V-ATPase that plays an important role in the regulation of acid-base balance by the kidney is a multisubunit enzyme that is densely packed into specialized membrane domains in intercalated cells. Intercalated cells can be separated into at least two subtypes, A-cells and B-cells, based on their morphological features, the distribution of V-ATPase, and the presence or absence of a basolateral chloride/bicarbonate anion exchanger (AE1) exclusively in B-cells. A-cells secrete protons into the tubule lumen, whereas B-cells secrete bicarbonate. The relative amounts of V-ATPase and AE1 in the plasma membranes of A- and B-cells are modulated under different acid-base conditions and provide a sensitive means by which urinary acidification can be controlled. The mechanisms governing the movement of acid-base transporting proteins between intracellular vesicles and the plasma membrane are under investigation. The microtubular apparatus of the cell is involved in maintaining both apical and basolateral polarity of the enzyme, and different isoforms of V-ATPase subunits may also be involved in the selective targeting of V-ATPase to different membrane domains.

Acid-Base Equilibrium↗
PubMed1992

Hyoid bone involvement by squamous cell carcinoma: clinical and pathological features.

The incidence of hyoid bone involvement by neoplasia is undetermined, despite its importance in hyoid-preserving surgery. Eleven (1.46%) of 755 whole-organ laryngeal specimens examined demonstrated hyoid bone infiltration. These included 6 cases originating from the larynx, 3 from the vallecula, and 1 case each from the pyriform fossa and tongue base. Clinically, vallecular involvement was helpful in determining hyoid invasion; however, computed tomography (CT) was disappointing. The greater cornu was the sole site of invasion in six cases. Ten of 11 cases were secondary to direct tumor spread. All carcinomas were advanced, with variable differentiation. Vascular and neural invasion was a prominent feature. Hyoid bone invasion is rare, and associated with a poor prognosis. Hyoid bone preservation is feasible in a majority of patients.

Aged↗
PubMed1992

Glycosyl-phosphatidylinositol-anchored membrane proteins.

Many proteins of eukaryotic cells are anchored to membranes by covalent linkage to glycosyl-phosphatidylinositol (GPI). These proteins lack a transmembrane domain, have no cytoplasmic tail, and are, therefore, located exclusively on the extracellular side of the plasma membrane. GPI-anchored proteins form a diverse family of molecules that includes membrane-associated enzymes, adhesion molecules, activation antigens, differentiation markers, protozoan coat components, and other miscellaneous glycoproteins. In the kidney, several GPI-anchored proteins have been identified, including uromodulin (Tamm-Horsfall glycoprotein), carbonic anhydrase type IV, alkaline phosphatase, Thy-1, BP-3, aminopeptidase P, and dipeptidylpeptidase. GPI-anchored proteins can be released from membranes with specific phospholipases and can be recovered from the detergent-insoluble pellet after Triton X-114 treatment of membranes. All GPI-anchored proteins are initially synthesized with a transmembrane anchor, but after translocation across the membrane of the endoplasmic reticulum, the ecto-domain of the protein is cleaved and covalently linked to a preformed GPI anchor by a specific transamidase enzyme. Although it remains obscure why so many proteins are endowed with a GPI anchor, the presence of a GPI anchor does confer some functional characteristics to proteins: (1) it is a strong apical targeting signal in polarized epithelial cells; (2) GPI-anchored proteins do not cluster into clathrin-coated pits but instead are concentrated into specialized lipid domains in the membrane, including so-called smooth pinocytotic vesicles, or caveoli; (3) GPI-anchored proteins can act as activation antigens in the immune system; (4) when the GPI anchor is cleaved by PI-phospholipase C or PI-phospholipase D, second messengers for signal transduction may be generated; (5) the GPI anchor can modulate antigen presentation by major histocompatibility complex molecules. Finally, at least one human disease, paroxysmal nocturnal hemoglobinuria, is a result of defective GPI anchor addition to plasma membrane proteins.

Amino Acid Sequence↗
PubMed1992

Closely linked H2B genes in the marine copepod, Tigriopus californicus indicate a recent gene duplication or gene conversion event.

Two nonallelic histone gene clusters were characterized in the marine copepod, Tigriopus californicus. The DNA sequence of one of the clusters reveals six genes in the contiguous arrangement of H2B, H1, H3, H4, H2B and H2A. The order of genes within the second cluster is H3, H4, H2B and H2A. There is no evidence for the presence of an H1 gene in this cluster. Comparison of the three copepod H2B genes reveals a high degree of similarity between the 5' upstream regions and between the amino terminal halves of the two H2B genes found within the same cluster. From these data we infer that gene duplication and/or gene conversion events occurred within this cluster in the recent past.

Alleles↗
PubMed1992

Alternatives to gold.

Despite, or perhaps because of, its antiquity the lost wax casting process which we use in dentistry still produces the most accurate and durable restorations in our armamentarium. Although high-gold content alloys still act as the benchmark of quality, fit, and durability in the aggressive conditions of the mouth, their inherent cost, high density and low modulus have stimulated a search for alternatives. This has ranged widely through the metallurgical world and across the periodic table of the elements. As a result dental alloys for casting into inlays, crowns and bridges (with or without facings of dental porcelain) have become incredibly complex. This article will explain some of the reasons behind the developments.

Corrosion↗
PubMed1992

Vulvar vestibulitis: significant clinical variables and treatment outcome.

The subject of vulvar vestibulitis was reviewed in regard to clinical variables that may be associated with this problem as well as the success of available treatment modalities. Questionnaires were returned by 71 patients diagnosed as having vulvar vestibulitis. Identical information was obtained from a comparison group of individuals with no clinical or physical findings suggesting this diagnosis. A history of recurrent candidiasis and previous condyloma acuminatum were the only variables noted more frequently in patients with vestibulitis. Among the patients treated by perineoplasty, 66% reported complete or significant alleviation of vulvar pain; 78% of the women noted a significant decrease in dyspareunia. Of the patients treated with intralesional interferon, six (50%) reported significant improvement in dyspareunia. Vulvar vestibulitis is a puzzling clinical entity whose etiology is not well understood. Perineoplasty still appears to be the treatment of choice in properly selected individuals.

Adolescent↗
PubMed1992

[The determination of serum hepatitis B virus DNA by polymerase chain reaction in hepatitis B patients treated with alpha-interferon].

To clarify the status of HBV in serum of chronic hepatitis B (CHB) patients who were treated with alpha-interferon, we determined the serum HBV DNA before and after treatment in 15 CHB patients with polymerase chain reaction (PCR). Before treatment all the 15 patients were HBsAg and HBeAg positive. HBV DNA was also positive with dot-blot hybridization (DB), PCR, ethidium bromide (PCR-EB) and PCR Southern-blot hybridization (PCR-SBH). HBeAb was negative in all the 15 patients. 12 patients has the determination repeated 2 to 39 weeks after treatment, 7 out of the 12 patients became HBeAg negative and HBV DNA also negative with DB and PCR-EB. However, in 5 of the 7 patients HBV DNA was still positive with PCR-SBH. Seroconversion of HBeAb from negative to positive occurred in 4 of the 12, but HBV DNA of the 4 patients remained positive with PCR-SBH. After an interval of one and half year or more following treatment 12 patients repeated the examination, only 5 of the 12 patients became seronegative for HBeAg and HBV DNA with DB and PCR-EB, but in 4 of the 5 HBV DNA was positive with PCR-SBH. Two of the 5 were seropositive for HBeAb and HBV DNA with PCR-SBH. The mechanism of residual viraemia after alpha-interferon treatment in CHB patients is uncertain.

Adult↗
PubMed1992

Ethical issues in obstetric cases involving prematurity.

This article explores the ethical issues confronted when the process of childbirth is threatened by premature labor and delivery. In this article, obstetric ethics are distinguished within the larger study of "ethics," frameworks for decision making are critiqued, and factors that frequently influence the formation of ethical judgments are commented on.

Choice Behavior↗