42 research outputs found

    Radial heat transfer at the wall in packed beds.

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    A literature survey indicates that adequate mathematical models are available for the study of heat transfer in packed beds. However, experimental data have been obtained at low Reynolds numbers only, below 3500. Experimental results are reported for a 7 in. diameter bed packed with 0.489 in. and 0.658 in. diameter glass spheres, with preheated air as the fluid flowing in the bed. Results indicate that the bed-to-wall heat transfer coefficient hw, based on the wall temperature and a bulk gas temperature, may be best correlated by the relation Nu = 2.35 Re 0.63 to a standard deviation of 11.4 per cent for values between 2,000 and 15,000

    Secretin facilitates GABA transmission in the cerebellum

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    Secretin was the first hormone discovered in human history, and yet, its function as a neuropeptide has been overlooked in the past. The recent discovery of the potential use of secretin in treating autistic patients, together with the conflicting reports on its effectiveness, urges an in-depth investigation of this issue. We show here that in the rat cerebellar cortex, mRNAs encoding secretin are localized in the Purkinje cells, whereas those of its receptor are found in both Purkinje cells and GABAergic interneurons. Immunoreactivity for secretin is localized in the soma and dendrites of Purkinje cells. In addition, secretin facilitates evoked, spontaneous, and miniature IPSCs recorded from Purkinje cells. We propose that secretin is released from the somatodendritic region of Purkinje cells and serves as a retrograde messenger modulating GABAergic afferent activity.published_or_final_versio

    Molecular evolution of vertebrate VIP receptors and functional characterization of a VIP receptor from goldfish Carassius auratus

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    Vasoactive intestinal polypeptide (VIP) is a neuropeptide that has numerous physiological actions and is widely distributed in the body. However, as yet, there is no sequence information about VIP receptors in lower vertebrates. Partial cDNA fragments spanning transmembrane domains 2 to 6 of VIP receptors were isolated from six nonmammalian vertebrate species, including chicken, pigeon, frog, lizard, salmon, and goldfish. Sequence comparison of these receptors revealed essential structural motifs responsible for receptor function. In addition, the first nonmammalian full- length VIP receptor cDNA was obtained by screening a goldfish brain and pituitary cDNA library. Functional expression of this receptor in mammalian COS-7 cells showed that it is coupled to cAMP production in a VIP and PACAP concentration-dependent manner; the EC 50 of VIP was determined to be 1 nM. At 100 nM peptide, the relative potency of various peptides in stimulating cAMP in the transfected cells was VIP > PACAP > GHRH = secretin > PHM > PTH > glucagon > GLP-1 > GIP. Characterization of the VIP receptors in lower vertebrates should enhance our understanding of the molecular evolution and physiology of VIP in vertebrates.link_to_subscribed_fulltex

    Classification of functional motifs of the secretin receptor on signal transduction

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    Recently, secretin has been suggested as a neuropeptide and is be involved in autism and other diseases such as pancreatic adenomas. Thus, its biological functions and relationships with diseases have become a research focus. Therefore, understanding the signal transduction through secretin receptor is a pre-requisite for further investigation and interpretation. Secretin receptor has a relatively large N-terminal domain containing N-glycoslation sites for ligand recognition and conserved cysteine residues for receptor conformations. As one of the G protein coupled receptors, secretin receptor also contains the common molecular architecture of 7 transmembrane domains that intertwined by 3 exoloops and 3 endoloops. These transmemrbane domains were enriched by hydrophobic residues, which help to anchor the receptor into the plasma membrane. Whereas, many conserved basic residues were located in the 2nd and 3rd endoloops and proved to be involved in receptor activation and G protein coupling. Nevertheless, receptor signaling is a complicated process and the interaction and selectivity of G proteins that certainly rely on a combination of functional motifs. For the Carboxyl tail, conflicting research findings were published in the aspect of secretin receptor internalization and desensitization. In this article, we summarize the research studies and implications on function motifs of the secretin receptor and hence provide a general picture on its function

    Functional segregation of the highly conserved basic motifs within the third endoloop of the human secretin receptor

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    In this study, a mutagenesis-based strategy was employed to assess the roles of two highly conserved motifs (KLR and RLAR) within the third endoloop of the human secretin receptor. Block deletion of KLRT and mutation of Lys323 (K323I) significantly reduced cAMP accumulation, and these mutations did not affect ligand interaction and receptor number expressed on the cell surface. Thus, the KLRT region at the N terminus of the third endoloop, particularly Lys323, is important for G protein coupling. For the RLAR motif, receptors with substitutions at positions 339 and 342 from Arg to Ala (R339, 342A), Glu (R339, 342E), or Ile (R339, 342I) as well as block deletion of the RLAR motif were all found to be defective in both secretin-binding and cAMP production. Interestingly, a single mutation at the corresponding positions of Arg339 or Arg342 responded as the wild-type human secretin receptor in all functional assays, indicating that the presence of one Arg at either position within the RLAR motif is sufficient for a normal receptor function. Immunofluorescent staining of these mutant receptors showed that these Arg residues are responsible for surface presentation and/or receptor stability.link_to_subscribed_fulltex

    Identification and characterization of a receptor from goldfish specific for a teleost growth hormone-releasing hormone-like peptide

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    In mammals, growth hormone-releasing hormone (GHRH), acting via the GHRH receptor, plays an important role in the regulation of growth hormone (GH) synthesis and secretion as well as the proliferation and differentiation of somatotropes in the pituitary. In fishes, information concerning the functional role of the characterized GHRHs is limited. For that reason, a putative goldfish GHRH receptor cDNA was characterized in this study. The receptor cDNA is 2243 bp in length, encoding a 438-amino-acid-long polypeptide with 7 putative transmembrane-spanning regions, which is a characteristic of G-protein-coupled receptors. The receptor, when expressed in COS-7 cells, showed minimal responses (2-fold cAMP responses) when stimulated with 100 nM of human GHRH, pituitary adenylate cyclase-activating polypeptide (PACAP) and vasoactive intestinal polypeptide (VIP). However, this receptor was found to be specific for a carp GHRH-like peptide isolated from the brain of common carp (Cyprinus carpio); there was a significant and dose-dependent increase in intracellular cAMP (a maximum response of 22-fold increase with an EC 50 Of 0.1 nM) when the transfected cells were stimulated with this peptide. As a preliminary study to investigate the functional role of this receptor, the tissue distribution of the mRNA was analyzed by reverse-transcription-polymerase chain reaction. The receptor mRNA was found to be present in the brain, pituitary, gut, gill, heart, liver, skeletal muscle, spleen, ovary and testis. Together with a goldfish PACAP type 1 receptor and a VIP1 receptor recently isolated in our laboratory, characterization of this putative GHRH receptor provides the molecular basis for the future understanding of the neuroendocrine control of growth and reproduction by these neuropeptides in goldfish as well as other teleosts.link_to_subscribed_fulltex

    Molecular cloning and mRNA Distribution of pituitary adenylate cyclase-activating polypeptide (PACAP)/PACAP-related peptide in the lungfish

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    In this article, we report the isolation of a full-length cDNA clone encoding pituitary adenylate cyclase-activating polypeptide (PACAP)/PACAP- related peptide (PRP) from lungfish Protopterus dolloi. When comparing the deduced amino acid sequences, the lungfish PACAP was found to be highly conserved with other vertebrates; however, the PRP shares only lower levels of sequence identity with known PRP sequences. Consistently in phylogenetic analysis, the lungfish PRP, similar to sturgeon PRP, fails to cluster with other PRPs. In addition to the full-length clone, another cDNA encoding a short precursor that lacks the first 32 amino acids of the PRP was also isolated. Interestingly, similar isoforms were also identified in several nonmammalian vertebrates, and it was suggested that exon skipping of PRP/PACAP transcripts was a mechanism that regulated the expression ratio of PACAP to PRP in nonmammalian vertebrates. By real-time PCR, both long and short PRP/PACAP transcripts were found almost exclusively in the brain, and the short isoform is the more abundant transcript (3.7 times more), indicating that PACAP is the major product produced in lungfish brain. The expression patterns of lungfish and previously studied frog PRP/PACAP suggest that the PRP/PACAP gene in the tetrapod lineage may first express in the central nervous system; in the process of evolution, the functions of these peptides diversified and were later found in other tissues. © 2009 New York Academy of Sciences.link_to_subscribed_fulltex
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