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Biomedical subjects

S Collins

Publications and source records attributed to S Collins.

At least 199 records · Page 11Linked to original sources
PubMed1992

Distribution of mast cells in intestinal muscle of nematode-sensitized rats.

We examined the distribution and functional integrity of mast cells in intestinal longitudinal muscle in rats sensitized by two previous infections with Trichinella spiralis. A segment of jejunum was excluded from the gut before infection, and the remainder of the gut was anastomosed. Few mast cells were seen in muscle of noninfected control rats except in the region of the jejunal anastomosis. In rats sensitized by T. spiralis infection, mast cells were increased in number in the jejunum and the number of mast cells followed an aboral gradient down the entire length of the gut in continuity. In addition, mast cells were present in muscle of the excluded segment of sensitized rats. All mast cells were stained red with safranin. Functional integrity was assessed by the ability of mast cells to induce contraction after degranulation by antigen. In muscle from sensitized rats, contraction was induced in each region after exposure to T. spiralis antigen but not Nippostrongylus brasiliensis antigen. Contraction was inhibited by the mast cell stabilizer doxantrazole and the 5-hydroxytryptamine (5-HT) antagonist cyproheptadine. When antigen-induced contraction was expressed as a percentage of the maximum response of the tissue to exogenous 5-HT, the magnitude of contraction decreased along an aboral gradient down the intestine and correlated well (r2 = 0.878) with mast cell numbers. These results suggest that the increase in connective tissue mast cells in gut muscle after T. spiralis infection involves both local and systemic mechanisms.

Animals↗
PubMed1991

Mitochondrial genome distribution in histochemically cytochrome c oxidase-negative muscle fibres in patients with a mixture of deleted and wild type mitochondrial DNA.

In situ hybridization studies were performed on a series of chronic progressive external ophthalmoplegia patients harbouring large mitochondrial DNA deletions, using intra- and extra-deletional probes. Clear differences in the distribution of wild type and deleted mitochondrial genomes were seen in both ragged-red and non-ragged red, cytochrome c oxidase-negative fibres, with an accumulation of deleted genomes in the subsarcolemmal zone. Wild type genome content was normal or decreased in the cytochrome c oxidase-negative regions of one case, but in two patients, wild type mtDNA content in cytochrome c oxidase-negative regions was either normal (most fibres) or increased (occasional fibres). The latter observation suggests there may be a stage in the natural history of ragged-red fibre evolution where wild type genomes are transiently increased. The significance of this finding is discussed.

Base Sequence↗
PubMed1991

Hem-1, a potential membrane protein, with expression restricted to blood cells.

Overlapping cDNAs 3.8 kb in length containing a long open reading frame were obtained that hybridized exclusively to transcripts from hematopoietic cells. Sequence analysis found eight potential membrane domains and two possible cAMP/cGMP phosphorylation sites. This sequence exhibited no homologies with the EMBL/Genbank nucleic acid, SwissProt or GenPept amino acid data bases. The gene is located at 12q13.1, a region of occasional translocations in hematopoietic neoplasia and a rare folic acid fragile site, Fra 12A.

Animals↗
PubMed1991

Chronic progressive external ophthalmoplegia in patients with large heteroplasmic mitochondrial DNA deletions: an immunocytochemical study.

Immunocytochemical studies with a holocomplex antibody battery in patients with chronic progressive external ophthalmoplegia, with and without large mitochondrial DNA deletions, revealed positive (and often increased) immunoreactivity for all complexes studied in histochemically cytochrome oxidase (COX)-negative areas, suggesting a compensatory up-regulation of these components. Similar findings were observed with subunit-specific probes directed against both nuclear- and mitochondrially encoded gene products. Comparison of staining intensities between the different complexes revealed significantly more variability in COX-negative than COX-positive fibres, suggesting disordered stoichiometric control during up-regulation. These differences were confirmed using statistical models. This data challenges the view that COX-negative fibre segments have little or no mitochondrially coded protein translation.

Adult↗
PubMed1991

Biochemical and molecular investigation of mitochondrial disease: an illustrative case showing the value of a multifaceted approach.

Detailed biochemical and molecular investigations in a patient with Kearns-Sayre syndrome are presented. Polarographic studies in isolated mitochondria revealed a global impairment in respiratory capacity consistent with an admixture of functional and non-functional mitochondria. Cytochrome difference spectra revealed a selective deficiency in cytochrome aa3. Western immunoblot studies revealed normal subunit content of Complexes I, III and IV. Southern blot studies of mtDNA showed a deletion of approximately 5 Kb coexisting with wild type DNA. PCR analysis confirmed that this deletion lies between the ATPase8 and NAD coenzyme Q oxidoreductase subunit 5 (ND5) genes. Breakpoint sequencing revealed a 13 nucleotide direct repeat flanking sequence (ACCTCCCTCACCA) consistent with slippage in mtDNA during replication as the mechanism of deletion. Histochemical studies of skeletal muscle revealed many cytochrome oxidase negative fibres and immunocytochemical studies showed cytochrome oxidase negative areas with abundant respiratory complex protein suggesting upregulation. The value of a multifaceted approach in unravelling the pathophysiology of mitochondrial diseases is emphasised.

Adolescent↗
PubMed1991

Regulation of adrenergic receptor responsiveness through modulation of receptor gene expression.

Multiple mechanisms contribute to the regulation of G protein-coupled receptors and their transmembrane signaling. Post-translational modifications of the receptors, such as phosphorylation, and changes in receptor gene expression can occur in either a strictly agonist-dependent fashion or through second messenger-mediated autoregulation. We have shown that modulation of receptor gene expression contributes to the responsiveness of adrenergic and related receptors. Recent evidence for post-transcriptional regulation, as well as the stimulation of transcription in an autoregulatory manner, indicates the unanticipated variety and complexity of mechanisms regulating adrenergic receptor responsiveness.

Animals↗
PubMed1990

A cAMP response element in the beta 2-adrenergic receptor gene confers transcriptional autoregulation by cAMP.

The rate of transcription of the beta 2-adrenergic receptor gene is increased in response to beta-adrenergic agonist stimulation of the receptor at the cell surface. This effect is mediated by stimulation of adenylyl cyclase and elevation of intracellular cAMP levels. We have previously shown that this responsiveness to cAMP resides in the 5'-flanking region of the human beta 2-adrenergic receptor gene (Collins, S., Bouvier, M., Bolanowski, M. A., Caron, M. G., and Lefkowitz, R. J. (1989) Proc. Natl. Acad. Sci. U. S. A. 86, 4853-4857). A 34-base pair sequence derived from the beta 2-adrenergic receptor promoter region (-70 to -37 base pairs), containing the sequence GTACGTCA, confers responsiveness to cAMP when present in either orientation 5' to the thymidine kinase promoter on the chloramphenicol acetyltransferase reporter gene. Overexpression of the catalytic subunit of protein kinase A fully substituted for forskolin in inducing expression through this sequence, indicating that the cAMP induction is mediated through this kinase. Mutations within the GTACGTCA sequence completely abolished the stimulation. A 43-kDa transcription factor (cAMP response element-binding protein) confers cAMP responsiveness through binding to specific sequences. In gel mobility shift assays, purified cAMP response element-binding protein bound to the 34-base pair oligonucleotide from the beta 2-adrenergic receptor gene with an affinity similar to that for the well-characterized cAMP response element from the human glycoprotein hormone alpha-subunit gene, and failed to bind to mutated elements. Thus, positive autoregulation of the beta 2-adrenergic receptor gene appears to occur through receptor-mediated stimulation of adenylyl cyclase, with consequent activation of cAMP response element-binding protein and stimulation of beta 2-adrenergic receptor gene transcription. These results demonstrate a novel mechanism by which a receptor (beta 2-adrenergic receptor) stimulatory for adenylyl cyclase can exert positive feedback regulation on its own expression.

Animals↗
PubMed1990

Alpha 1-adrenergic receptor mRNA level is regulated by norepinephrine in rabbit aortic smooth muscle cells.

Prolonged agonist exposure results in a decrease in the density of alpha 1-adrenergic receptors in rabbit aortic smooth muscle cells. A cDNA for the alpha 1-adrenergic receptor was used to assess the effect of norepinephrine on alpha 1-adrenergic receptor mRNA level in cultured vascular smooth muscle cells from the rabbit aorta. Norepinephrine caused a transient decrease (81% +/- 5%; n = 9) in alpha 1-adrenergic receptor mRNA. The effect was concentration dependent (EC50, approximately 0.3 microM; maximal effect, 10 microM). The maximum decrease occurred after 4 hr of exposure to norepinephrine and was followed by a gradual return to control levels by 24 hr. The decrease in mRNA level was blocked by prazosin, but not propranolol, and was mimicked by phenylephrine. These results indicate that the effect is mediated by stimulation of the alpha 1-adrenergic receptor and suggest that it involves one or more alpha 1-adrenergic-coupled second messenger pathways. The decrease in alpha 1-adrenergic receptor mRNA caused by norepinephrine exceeds that caused by actinomycin D, suggesting that norepinephrine may cause a decrease in the stability of alpha 1-adrenergic receptor mRNA. Actinomycin D also blocked the norepinephrine-induced decrease in mRNA level, further suggesting that the effect of norepinephrine requires induction of transcription, presumably leading to synthesis of a labile factor that is necessary for the effect of norepinephrine on alpha 1-adrenergic receptor mRNA level.

Animals↗
PubMed1990

The value of youth: equalizing age differentials in marriages.

"The objective of this paper is to present a model of constrained utility-maximizing behaviour which is able to explain several features of marriage. The model predicts that individuals meet in the marriage market and trade characteristics, in which they are relatively well endowed, to obtain characteristics in which they are less well endowed. The model implies a positive age differential in favour of the husband due to biological differences. This differential is shown to be attentuated by differences in earnings capacity and human capital investments. The model also has implications for dynamic aspects of marriage and provides an explanation for the secular increase in females' age of first marriage and difficulty experienced by females in the post thirty-year age group in finding suitable partners. An examination of unit record data on residents of metropolitan California from the 1980 United States Census reveals systematic patterns in the data are consistent with the theory."

Age Factors↗
PubMed1990

Expression of three alpha 2-adrenergic receptor subtypes in rat tissues: implications for alpha 2 receptor classification.

Based on biochemical and ligand binding studies in various tissues and species, evidence for several alpha 2-adrenergic receptor subtypes has accumulated. The current alpha 2-adrenergic receptor classification (alpha 2A, alpha 2B, alpha 2C) is based exclusively on pharmacological criteria. The molecular cloning of three distinct genes for human alpha 2-adrenergic receptors has confirmed the existence of multiple alpha 2-adrenergic receptor subtypes. According to their localization on different human chromosomes, the receptor genes were termed alpha 2-C10, alpha 2-C4, and alpha 2-C2. The relationship, however, between the pharmacologically characterized alpha 2-adrenergic receptors and the isolated genes has yet to be clarified. Using Northern blot hybridization, we analyzed the expression of the three cloned alpha 2-adrenergic receptor genes in 13 rat tissues, as well as in cell lines previously described as model systems for the pharmacologically defined alpha 2-adrenergic receptor subtypes. The alpha 2-C10 receptor corresponds to the alpha 2A subtype and is expressed in rat brainstem, cerebral cortex, hippocampus, pituitary gland, cerebellum, kidney, aorta, skeletal muscle, spleen, and lung. Messenger RNA coding for the alpha 2-C4 receptor was detected only in brain regions, not in peripheral tissues, whereas the alpha 2-C2 message was found only in liver and kidney. Hybridization experiments with RNA derived from tissues and cells from which the pharmacological alpha 2-receptor classification has been developed lead to the conclusion that the alpha 2B subtype represents two distinct receptor molecules, the alpha 2-C4 and a subtype previously undetected by classical ligand binding approaches. Furthermore, our results suggest that the alpha 2C subtype characterized in opossum kidney cells is an interspecies variation of alpha 2-C4 rather than a separate subtype. Finally, the cloned alpha 2-C2 receptor was found to be "alpha 2B-like" and not covered by the current pharmacological classification.

Animals↗
PubMed1990

Chancroid: results from an outbreak in Houston, Texas.

A recent (and continuing) epidemic of chancroid in Houston has included morphologic variation in the disease, including so-called dwarf, classic, giant, transient, follicular, phagedenic, and pseudogranuloma inguinale types. Most cases were clearly acquired by unprotected sexual encounters with local prostitutes. The strain of Haemophilus ducreyi responsible for this outbreak was relatively easily cultured on routine media; unexpected sensitivity of this strain to vancomycin rendered the recommended "selective" growth medium much less optimal for isolation. Therapeutic success uniformly followed the use of intramuscular ceftriaxone sodium; one case responded to oral ciprofloxacin hydrochloride.

Administration, Oral↗
PubMed1989

Two distinct pathways for cAMP-mediated down-regulation of the beta 2-adrenergic receptor. Phosphorylation of the receptor and regulation of its mRNA level.

We have studied cyclic AMP-mediated regulation of the beta 2-adrenergic receptor (beta 2AR). The effects of cAMP were assessed in Chinese hamster fibroblast (CHW) cells expressing either the wild type human beta 2AR receptor (CH-beta 2) or mutated forms of the receptor lacking the consensus sequences for phosphorylation by the cAMP-dependent protein kinase. Treatment of the CH-beta 2 cells with the cAMP analogue dibutyryl cAMP (Bt2cAMP) induces a time-dependent "down-regulation" of the number of beta 2AR. This down-regulation of the receptors is accompanied by a decline in the steady state level of beta 2AR mRNA. Moreover, the treatment with Bt2cAMP induces an increase in the phosphorylation level of the membrane-associated beta 2AR. Both the reduction in beta 2AR mRNA and the enhanced phosphorylation of the receptor are rapid and precede the loss of receptor. The down-regulation of beta 2AR induced by Bt2cAMP is concentration-dependent and mimicked by the other biologically active cyclic nucleotide analogue, 8-Br-cAMP, by forskolin, and by the phosphodiesterase inhibitor, isobutylmethylxanthine. In the CHW cell lines expressing receptors lacking the putative protein kinase A phosphorylation sites, the Bt2cAMP-induced phosphorylation of beta 2AR is completely abolished. In these cells the down-regulation of beta 2AR receptor number produced by cAMP is significantly slowed, whereas the reduction in beta 2AR mRNA level is equivalent to that observed in CH-beta 2 cells. These data indicate that there are at least two pathways by which cAMP may decrease the number of beta 2ARs in cells: one involves phosphorylation of the receptor by the cAMP-dependent protein kinase and the other leads to a reduction in steady state beta 2AR mRNA levels.

1-Methyl-3-isobutylxanthine↗
PubMed1989

cAMP stimulates transcription of the beta 2-adrenergic receptor gene in response to short-term agonist exposure.

In addition to conveying cellular responses to an effector molecule, receptors are often themselves regulated by their effectors. We have demonstrated that epinephrine modulates both the rate of transcription of the beta 2-adrenergic receptor (beta 2AR) gene and the steady-state level of beta 2AR mRNA in DDT1MF-2 cells. Short-term (30 min) exposure to epinephrine (100 nM) stimulates the rate of beta 2AR gene transcription, resulting in a 3- to 4-fold increase in steady-state beta 2AR mRNA levels. These effects are mimicked by 1 mM N6,O2'-dibutyryladenosine 3',5'-cyclic monophosphate (Bt2cAMP) or foskolin but not by phorbol esters. The half-life of the beta 2AR mRNA after addition of actinomycin D (46.7 +/- 10.2 min; mean +/- SEM; n = 5) remained unchanged after 30 min of epinephrine treatment (46.8 +/- 10.6 min; mean +/- SEM; n = 4), indicating that a change in transcription rate is the predominant factor responsible for the increase of beta 2AR mRNA. Whereas brief exposure to epinephrine or Bt2cAMP does not significantly affect the total number of cellular beta 2ARs (assessed by ligand binding), continued exposure results in a gradual decline in beta 2AR number to approximately 20% (epinephrine) or approximately 45% (Bt2cAMP) of the levels in control cells by 24 hr. Similar decreases in agonist-stimulated adenylyl cyclase activity are observed. This loss of receptors with prolonged agonist exposure is accompanied by a 50% reduction in beta 2AR mRNA. Transfection of the beta 2AR promoter region cloned onto a reporter gene (bacterial chloramphenicol acetyltransferase) allowed demonstration of a 2- to 4-fold induction of transcription by agents that elevate cAMP levels, such as forskolin or phosphodiesterase inhibitors. These results establish the presence of elements within the proximal promoter region of the beta 2AR gene responsible for the transcriptional enhancing activity of cAMP and demonstrate that beta 2AR gene expression is regulated by a type of feedback mechanism involving the second messenger cAMP.

1-Methyl-3-isobutylxanthine↗