Percorrer por autor "Renfro, J. Larry"
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- Active removal of inorganic phosphate from cerebrospinal fluid by the choroid plexusPublication . Guerreiro, Pedro; Bataille, Amy M.; Parker, Sonda L.; Renfro, J. LarryThe P-i concentration of mammalian cerebrospinal fluid (CSF) is about one-half that of plasma, a phenomenon also shown here in the spiny dogfish, Squalus acanthias. The objective of the present study was to characterize the possible role of the choroid plexus (CP) in determining CSF P-i concentration. The large sheet-like fourth CP of the shark was mounted in Ussing chambers where unidirectional P-33(i) fluxes revealed potent active transport from CSF to the blood side under short-circuited conditions. The flux ratio was 8: 1 with an average transepithelial resistance of 87 +/- 17.9 Omega . cm(2) and electrical potential difference of + 0.9 +/- 0.17 mV (CSF side positive). Active P-i absorption from CSF was inhibited by 10 mM arsenate, 0.2 mM ouabain, Na+ -free medium, and increasing the K+ concentration from 5 to 100 mM. Li+ stimulated transport twofold compared with Na+-free medium. Phosphonoformic acid (1 mM) had no effect on active Pi transport. RT-PCR revealed both P-i transporter (PiT) 1 and PiT2 (SLC20 family) gene expression, but no Na+ -P-i cotransporter II (SLC34 family) expression, in the shark CP. PiT2 immunoreactivity was shown by immunoblot analysis and localized by immunohistochemistry in (or near) the CP apical microvillar membranes of both the shark and rat. PiT1 appeared to be localized primarily to vascular endothelial cells. Taken together, these data indicate that the CP actively removes P-i from CSF. This process has transport properties consistent with a PiT2, Na+-dependent transporter that is located in the apical region of the CP epithelium.
- Parathyroid hormone (PTH)-related protein stimulates Pi secretion across fish proximal tubule cellsPublication . Guerreiro, P. M.; Canario, Adelino V. M.; Power, Deborah; Renfro, J. LarryThe factors that control Ca2+ and Pi transport in the fish nephron are unclear. In tetrapods these ions are primarily regulated by calcitonin and PTH. Recently several PTH-like proteins were found in fish but their roles are not known. In fish larvae, PTHrP enhanced total Ca2+ uptake, increasing influx and reducing efflux.
- Piscine PTHrP regulation of calcium and phosphate transport in winter flounder renal proximal tubule primary culturesPublication . Guerreiro, P. M.; Canario, Adelino V. M.; Power, Deborah; Renfro, J. LarryMultiple factors control calcium (Ca2 ) and inorganic phosphate (Pi) transport in the fish nephron, and the recently discovered members of the piscine parathyroid hormone-like protein family are likely participants in such regulatory mechanisms. The effects of an NH2-terminal peptide (amino acids 1–34) of Takifugu rubripes parathyroid hormone-related protein, (1–34)PTHrP, on Ca2 and Pi transport were investigated in winter flounder (Pseudopleuronectes americanus) proximal tubule cells in primary culture (fPTCs). RT-PCR performed on RNA extracted from fPTCs and from intact kidney tissue indicated that expression of PTHrP and types 1 and 3 PTH/PTHrP receptors occurred both in vivo and in vitro and that circulating levels of PTHrP measured by specific radioimmunoassay averaged 2.5 0.13 ng/ml. fPTC monolayers were mounted in Ussing chambers, and under neutral electrochemical conditions, addition of 10 nM (1–34)PTHrP to the basolateral side induced a slight increase in Ca2 transport rate from luminal to peritubular side, significantly stimulating net Ca2 reabsorption. (1–34)PTHrP also significantly increased the Pi secretory flux, and slightly reduced Pi reabsorption, evoking a significant increase in Pi net secretion. This stimulatory effect was partially inhibited by bisindolylmaleimide, an inhibitor of protein kinase C. Incubation of ex vivo flounder renal tubules with (1–34)PTHrP resulted in apparent reduction of Na -Pi cotransporter type II (NaPi-II) protein in tubule membranes. PTHrP seems therefore to participate in the modulation of Ca2 and Pi homeostasis by fish kidney.
- The parathyroid hormone family of peptides: structure, tissue distribution, regulation, and potential functional roles in calcium and phosphate balance in fishPublication . Guerreiro, P. M.; Renfro, J. Larry; Power, Deborah; Canario, Adelino V. M.Parathyroid hormone (PTH) and PTH-related protein (PTHrP) are two factors that share amino acid sequence homology and act via a common receptor. In tetrapods, PTH is the main endocrine factor acting in bone and kidney to regulate calcium and phosphate. PTHrP is an essential paracrine developmental factor present in many tissues and is involved in the regulation of ossification, mammary gland development, muscle relaxation, and other functions. Fish apparently lack an equivalent of the parathyroid gland and were long thought to be devoid of PTH. Only in recent years has the existence of PTH-like peptides and their receptors in fish been firmly established. Two forms of PTH, two of PTHrP, and a protein with intermediate characteristics designated PTH-L are encoded by separate genes in teleost fish. Three receptors encoded by separate genes in fish mediate PTH/PTHrP actions, whereas only two receptors have so far been found in terrestrial vertebrates. PTHrP has been more intensively studied than PTH, from lampreys to advanced teleosts. It is expressed in many tissues and is present in high concentration in fish blood. Administration of this peptide alters calcium metabolism and has marked effects on associated gene expression and enzyme activity in vivo and in vitro. This review provides a comprehensive overview of the physiological roles, distribution, and molecular relationships of the piscine PTH-like peptides.