101
|
Amstrup J, Frøslev J, Willumsen NJ, Møbjerg N, Jespersen A, Larse EH. Expression of cystic fibrosis transmembrane conductance regulator in the skin of the toad, Bufo bufo and possible role for Cl- transport across the heterocellular epithelium. Comp Biochem Physiol A Mol Integr Physiol 2001; 130:539-50. [PMID: 11913465 DOI: 10.1016/s1095-6433(01)00432-9] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/18/2022]
Abstract
Evidence is discussed that apical CFTR Cl- channels of mitochondria-rich (MR) cells of Bufo bufo skin conduct beta-adrenergic receptor-activated Cl- currents. Ussing chambers studies revealed the following selectivity sequence of the receptor activated conductance, Cl- > Br- > NO3- > I-. With ion selective microelectrode-techniques, it was shown that receptor-coupled Cl- channels are not located in principal cells. A small conductance (7-10 pS) CFTR-like Cl- channel is located in the apical plasma membrane of MR cells. Short life times of sealed patches prevented detailed study of its selectivity to other halide ions and its molecular regulation. With monoclonal hCFTR-antibodies, selective expression in MR cells of the targeted antigens could be demonstrated. A transcript of CFTR was amplified in the skin, and a bbCFTR cDNA clone was generated from toad skin mRNA that exhibits 89% amino acid identity with the human homologue. The frequency of obtaining channels in patch clamp studies was too low for accounting quantitatively for the macroscopic conductance. Since MR cells were isolated by trypsin, and a putative extracellular loop of the deduced bbCFTR protein contains a target peptide bond for trypsin, enzyme treatment may have destroyed apical CFTR molecules.
Collapse
Affiliation(s)
- J Amstrup
- Zoophysiological Laboratory, August Krogh Institute, The University of Copenhagen, Denmark
| | | | | | | | | | | |
Collapse
|
102
|
Cutler CP, Cramb G. Molecular physiology of osmoregulation in eels and other teleosts: the role of transporter isoforms and gene duplication. Comp Biochem Physiol A Mol Integr Physiol 2001; 130:551-64. [PMID: 11913466 DOI: 10.1016/s1095-6433(01)00435-4] [Citation(s) in RCA: 52] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/16/2022]
Abstract
This review focuses on recent developments in the molecular biology of ion and water transporter genes in fish and the potential role of their products in osmoregulation in both freshwater and seawater environments. In particular details of isoforms of various ATPases, co-transporters, exchangers and ion channels in the eel as well as other teleost species are described. Many of the teleost transporter isoforms discovered so far, appear to occur as twin or duplicate copies compared to their homologous counterparts in higher vertebrates, although these duplicate isoforms often have distinct tissue-specific and developmental stage-dependent expression patterns. The possible meaning of this information will be examined in relation to the fish genome duplication debate.
Collapse
Affiliation(s)
- C P Cutler
- School of Biology, University of St Andrews, Fife, UK.
| | | |
Collapse
|
103
|
Chen JM, Cutler C, Jacques C, Boeuf G, Denamur E, Lecointre G, Mercier B, Cramb G, Férec C. A combined analysis of the cystic fibrosis transmembrane conductance regulator: implications for structure and disease models. Mol Biol Evol 2001; 18:1771-88. [PMID: 11504857 DOI: 10.1093/oxfordjournals.molbev.a003965] [Citation(s) in RCA: 58] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/19/2022] Open
Abstract
Over the past decade, nearly 1,000 variants have been identified in the cystic fibrosis transmembrane conductance regulator (CFTR) gene in classic and atypical cystic fibrosis (CF) patients worldwide, and an enormous wealth of information concerning the structure and function of the protein has also been accumulated. These data, if evaluated together in a sequence comparison of all currently available CFTR homologs, are likely to refine the global structure-function relationship of the protein, which will, in turn, facilitate interpretation of the identified mutations in the gene. Based on such a combined analysis, we had recently defined a "functional R domain" of the CFTR protein. First, presenting two full-length cDNA sequences (termed sCFTR-I and sCFTR-II) from the Atlantic salmon (Salmo salar) and an additional partial coding sequence from the eastern gray kangaroo (Macropus giganteus), this study went further to refine the boundaries of the two nucleotide-binding domains (NBDs) and the COOH-terminal tail (C-tail), wherein NBD1 was defined as going from P439 to G646, NBD2 as going from A1225 to E1417, and the C-tail as going from E1418 to L1480. This approach also provided further insights into the differential roles of the two halves of CFTR and highlighted several well-conserved motifs that may be involved in inter- or intramolecular interactions. Moreover, a serious concern that a certain fraction of missense mutations identified in the CFTR gene may not have functional consequences was raised. Finally, phylogenetic analysis of all the full-length CFTR amino acid sequences and an extended set of exon 13--coding nucleotide sequences reinforced the idea that the rabbit may represent a better CF model than the mouse and strengthened the assertion that a long-branch attraction artifact separates the murine rodents from the rabbit and the guinea pig, the other Glires.
Collapse
Affiliation(s)
- J M Chen
- Institut National de la Santé et de la Recherche Médicale EMI 01 15, Etablissement Français du Sang-Bretagne, Universite de Bretagne Occidentale, and Centre Hospitalier Universitaire, Brest, France
| | | | | | | | | | | | | | | | | |
Collapse
|
104
|
Kültz D, Chakravarty D, Adilakshmi T. A novel 14-3-3 gene is osmoregulated in gill epithelium of the euryhaline teleost Fundulus heteroclitus. J Exp Biol 2001; 204:2975-85. [PMID: 11551986 DOI: 10.1242/jeb.204.17.2975] [Citation(s) in RCA: 50] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Abstract
SUMMARY
We have cloned and analyzed the full-length coding sequence and 3′ untranslated region (UTR) of a unique 14-3-3 gene of the euryhaline teleost Fundulus heteroclitus, which we named 14-3-3.a. Phylogenetic analysis of the deduced amino acid sequence revealed that the 14-3-3.a gene product is most similar to vertebrate 14-3-3ζ and β, yet it displays considerable divergence to known classes of vertebrate 14-3-3 isoforms. The N and C termini of 14-3-3.a are the most unique regions, whereas the amino acid residues forming the amphipathic ligand-binding groove are highly conserved. F. heteroclitus 14-3-3.a mRNA expression is high in gill epithelium, moderate in intestine and brain, and low in gonads, white muscle and heart. Because 14-3-3 proteins are important molecular scaffolds and cofactors for phosphoproteins and signaling complexes, the high level of 14-3-3.a expression in gill epithelium of the euryhaline teleost F. heteroclitus suggests that it is crucial for signal transduction in gill epithelial cells. We provide evidence that 14-3-3.a is involved in osmosensory signal transduction by showing that its mRNA and protein levels in gill epithelium, but not in any other tissue analyzed, increase two- to fourfold within 24h of salinity transfer of fish from sea water to fresh water. These data are clear evidence for an important role of 14-3-3.a in the remodeling of gill epithelium during transition of euryhaline fish between plasma-hyperosmotic and plasma-hyposmotic environments.
Collapse
Affiliation(s)
- D Kültz
- The Whitney Laboratory, University of Florida, 9505 Ocean Shore Boulevard, St Augustine, FL 32080, USA.
| | | | | |
Collapse
|
105
|
Daborn K, Cozzi RR, Marshall WS. Dynamics of Pavement Cell–Chloride Cell Interactions During Abrupt Salinity Change in FUNDULUS HETEROCLITUS. J Exp Biol 2001; 204:1889-99. [PMID: 11441031 DOI: 10.1242/jeb.204.11.1889] [Citation(s) in RCA: 74] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Abstract
SUMMARY
Freshwater-adapted killifish (Fundulus heteroclitus) opercular epithelia were dissected and subjected to blood-side hypertonic bathing solution in Ussing-style chambers to simulate the increase in blood osmolality during migration to sea water. Conversely, seawater-acclimated killifish opercular epithelia were subjected to hypotonic bathing solutions to simulate the initial stages of migration to fresh water. Freshwater-acclimation (hypertonic stress) induced a rapid (approximately 30min) increase in membrane conductance (Gt) from 3.10±0.56 to 7.52±1.15mScm−2 (P<0.01, N=27), whereas seawater-acclimation (hypotonic stress) induced a rapid decrease in Gt from 8.22±1.15 to 4.41±1.00mScm−2 (P<0.01, N=27; means ± s.e.m.). Control seawater-acclimated membranes had a density of apical crypts (where chloride cells are exposed to the environment; detected by scanning electron microscopy) of 1133±96.4cryptsmm−2 (N=12), whereas the hypotonically shocked specimens had a lower crypt density of 870±36.7cryptsmm−2 (P<0.01 N=10; means ± s.e.m.). Hypertonic shock of freshwater membranes increased crypt density from 383.3±73.9 (N=12) to 630±102.9cryptsmm−2 (P<0.05; N=11; means ± s.e.m.). There was no change in density of chloride cells, as detected by fluorescence microscopy; hence, osmotic stress changes the degree of exposure, not the number of chloride cells. Cytochalasin D (5.0μmoll−1) completely blocked the conductance response to hypotonic shock and the reduction in apical crypt density measured by scanning electron microscopy, while phalloidin (33μmoll−1), colchicine (3×10−4moll−1) and griseofulvin (1.0μmoll−1) were ineffective. Actin imaging by phalloidin staining and confocal microscopy revealed extensive actin cords in pavement cell microridges and a ring of actin at the apex of chloride cells. We conclude that the actin cytoskeleton of chloride cells is required to maintain crypt opening and that osmotic shock causes chloride cells to adjust their apical crypt size.
Collapse
Affiliation(s)
- K Daborn
- Biology Department, Saint Francis Xavier University, PO Box 5000, Antigonish, Nova Scotia, Canada B2G 2W5
| | | | | |
Collapse
|
106
|
Leguen I, Cravedi JP, Pisam M, Prunet P. Biological functions of trout pavement-like gill cells in primary culture on solid support: pH(i) regulation, cell volume regulation and xenobiotic biotransformation. Comp Biochem Physiol A Mol Integr Physiol 2001; 128:207-22. [PMID: 11223382 DOI: 10.1016/s1095-6433(00)00293-2] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/17/2022]
Abstract
This review presents results obtained on rainbow trout gill cells in primary culture on solid support. Ultrastructural analysis showed that cultured gill cells displayed features of pavement cells in situ. Several biological functions have been investigated on these cultured cells. First, it was shown that their intracellular pH at rest and after acidosis is regulated by a Na+/H+ exchanger. Second, gill cells in primary culture can regulate their volume after a cell swelling. Intracellular calcium appears to be involved in this regulation. The effects of different xenobiotics on the capacity of gill cells to regulate their volume are presented. Third, cultured pavement cells contain biotransformation enzymes to metabolize xenobiotics. All these results demonstrate that gill cells in primary culture on solid support represent a promising in vitro model for the study of pavement cells physiology. In conclusion, applications of this culture are discussed and compared with the permeable filter method, together with the limitations and prospects of this in vitro model on solid support.
Collapse
Affiliation(s)
- I Leguen
- INRA-SCRIBE, Physiologie de l'adaptation et du stress chez les poissons, IFR Reproduction, Development and Ecophysiology campus de Beaulieu, 35042, Rennes cedex, France.
| | | | | | | |
Collapse
|
107
|
Nikinmaa M, Salama A, Bogdanova A, Virkki LV. Beta-adrenergic stimulation of volume-sensitive chloride transport in lamprey erythrocytes. Physiol Biochem Zool 2001; 74:45-51. [PMID: 11226013 DOI: 10.1086/319307] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 08/16/2000] [Indexed: 11/03/2022]
Abstract
We measured the effects of a beta-adrenergic agonist, isoproterenol, on chloride transport and volume regulation of lamprey (Lampetra fluviatilis) erythrocytes in isotonic (288 mosm L(-1)) and hypotonic (192 mosm L(-1)) medium. Isoproterenol at a high concentration (10(-5) M) did not influence chloride transport in isotonic medium but markedly increased chloride fluxes in hypotonic conditions: unidirectional flux increased from 100 mmol kg dcw(-1) h(-1) in the absence to 350 mmol kg dcw(-1) h(-1) (dcw=dry cell weight) in the presence of isoproterenol. Simultaneously, the half-time for volume recovery decreased from 27 to 9 min. Isoproterenol caused an increase in cellular cyclic AMP (cAMP) concentration. The stimulation of chloride transport in hypotonic conditions could be induced by application of the permeable cAMP analogue, 8-bromo-cyclic AMP, suggesting that the effect of beta-adrenergic stimulation on chloride transport occurs downstream of cAMP production. As isoproterenol did not affect unidirectional rubidium fluxes in hypotonic conditions, the transport pathway influenced by beta-adrenergic stimulation is most likely the swelling-activated chloride channel. Because the beta-adrenergic agonist only influenced the transport in hypotonic conditions despite the fact that cAMP concentration also increased in isotonic conditions, the activation may involve a volume-dependent conformational change in the chloride channel.
Collapse
Affiliation(s)
- M Nikinmaa
- Department of Biology, University of Turku, FIN-20014 Turku, Finland.
| | | | | | | |
Collapse
|
108
|
Chen JM, Scotet V, Ferec C. Definition of a "functional R domain" of the cystic fibrosis transmembrane conductance regulator. Mol Genet Metab 2000; 71:245-9. [PMID: 11001817 DOI: 10.1006/mgme.2000.3041] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
The R domain of the cystic fibrosis transmembrane conductance regulator (CFTR) was originally defined as 241 amino acids, encoded by exon 13. Such exon/intron boundaries provide a convenient way to define the R domain, but do not necessarily reflect the corresponding functional domain within CFTR. A two-domain model was later proposed based on a comparison of the R-domain sequences from 10 species. While RD1, the N-terminal third of the R domain is highly conserved, RD2, the large central region of the R domain has less rigid structural requirements. Although this two-domain model was given strong support by recent functional analysis data, the simple observation that two of the four main phosphorylation sites are excluded from RD2 clearly indicates that RD2 still does not satisfy the requirements of a "functional R domain." Nevertheless, knowledge of the CFTR structure and function accumulated over the past decade and reevaluated in the context of a comprehensive sequence comparison of 15 CFTR homologues made it possible to define such a "functional R domain," i.e., amino acids C647 to D836. This definition is validated primarily because it contains all of the important potential consensus phosphorylation sequences. In addition, it includes the highly charged motif from E822 to D836. Finally, it includes all of the deletions/insertions in this region. This definition also aids in understanding the effects of missense mutations occurring within this domain.
Collapse
Affiliation(s)
- J M Chen
- Etablissement Français du Sang-Bretagne, Site de Brest, Brest, France
| | | | | |
Collapse
|
109
|
Davidson H, Taylor MS, Doherty A, Boyd AC, Porteous DJ. Genomic sequence analysis of Fugu rubripes CFTR and flanking genes in a 60 kb region conserving synteny with 800 kb of human chromosome 7. Genome Res 2000; 10:1194-203. [PMID: 10958637 PMCID: PMC310914 DOI: 10.1101/gr.10.8.1194] [Citation(s) in RCA: 20] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/06/2000] [Accepted: 06/02/2000] [Indexed: 12/13/2022]
Abstract
To define control elements that regulate tissue-specific expression of the cystic fibrosis transmembrane regulator (CFTR), we have sequenced 60 kb of genomic DNA from the puffer fish Fugu rubripes (Fugu) that includes the CFTR gene. This region of the Fugu genome shows conservation of synteny with 800-kb sequence of the human genome encompassing the WNT2, CFTR, Z43555, and CBP90 genes. Additionally, the genomic structure of each gene is conserved. In a multiple sequence alignment of human, mouse, and Fugu, the putative WNT2 promoter sequence is shown to contain highly conserved elements that may be transcription factor or other regulatory binding sites. We have found two putative ankyrin repeat-containing genes that flank the CFTR gene. Overall sequence analysis suggests conservation of intron/exon boundaries between Fugu and human CFTR and revealed extensive homology between functional protein domains. However, the immediate 5' regions of human and Fugu CFTR are highly divergent with few conserved sequences apart from those resembling diminished cAMP response elements (CRE) and CAAT box elements. Interestingly, the polymorphic polyT tract located upstream of exon 9 is present in human and Fugu but absent in mouse. Similarly, an intron 1 and intron 9 element common to human and Fugu is absent in mouse. The euryhaline killifish CFTR coding sequence is highly homologous to the Fugu sequence, suggesting that upregulation of CFTR in that species in response to salinity may be regulated transcriptionally.
Collapse
Affiliation(s)
- H Davidson
- Medical Research Council Human Genetics Unit, Western General Hospital, Edinburgh EH4 2XU, UK.
| | | | | | | | | |
Collapse
|
110
|
Wilson JM, Randall DJ, Donowitz M, Vogl AW, Ip AK. Immunolocalization of ion-transport proteins to branchial epithelium mitochondria-rich cells in the mudskipper (Periophthalmodon schlosseri). J Exp Biol 2000; 203:2297-310. [PMID: 10887068 DOI: 10.1242/jeb.203.15.2297] [Citation(s) in RCA: 140] [Impact Index Per Article: 5.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Abstract
The branchial epithelium of the mudskipper Periophthalmodon schlosseri is densely packed with mitochondria-rich (MR) cells. This species of mudskipper is also able to eliminate ammonia against large inward gradients and to tolerate extremely high environmental ammonia concentrations. To test whether these branchial MR cells are the sites of active ammonia elimination, we used an immunological approach to localize ion-transport proteins that have been shown pharmacologically to be involved in the elimination of NH(4)(+) (Na(+)/NH(4)(+) exchanger and Na(+)/NH(4)(+)-ATPase). We also investigated the role of carbonic anhydrase and boundary-layer pH effects in ammonia elimination by using the carbonic anhydrase inhibitor acetazolamide and by buffering the bath water with Hepes, respectively. In the branchial epithelium, Na(+)/H(+) exchangers (both NHE2- and NHE3-like isoforms), a cystic fibrosis transmembrane regulator (CFTR)-like anion channel, a vacuolar-type H(+)-ATPase (V-ATPase) and carbonic anhydrase immunoreactivity are associated with the apical crypt region of MR cells. Associated with the MR cell basolateral membrane and tubular system are the Na(+)/K(+)-ATPase and a Na(+)/K(+)/2Cl(−) cotransporter. A proportion of the ammonia eliminated by P. schlosseri involves carbonic anhydrase activity and is not dependent on boundary-layer pH effects. The apical CFTR-like anion channel may be serving as a HCO(3)(−) channel accounting for the acid-base neutral effects observed with net ammonia efflux inhibition.
Collapse
Affiliation(s)
- J M Wilson
- Department of Zoology, University of British Columbia, Vancouver, Canada V6T 1Z4.
| | | | | | | | | |
Collapse
|
111
|
Abstract
The cystic fibrosis transmembrane conductance regulator (CFTR) protein forms a Cl(−) channel found in the plasma membranes of many epithelial cells, including those of the kidney, gut and conducting airways. Mutation of the gene encoding CFTR is the primary defect in cystic fibrosis, a disease that affects approximately 30 000 individuals in the United States alone. Alteration of CFTR function also plays an important role in the pathophysiology of secretory diarrhea and polycystic kidney disease. The basic mechanisms of permeation in this channel are not well understood. It is not known which portions of the protein contribute to forming the pore or which amino acid residues in those domains are involved in the biophysical processes of ion permeation. In this review, I will discuss (i) the present understanding of ion transport processes in the wild-type CFTR channel, (ii) the experimental approaches currently being applied to investigate the pore, and (iii) a proposed structure that takes into account the present data on mechanisms of ion selectivity in the CFTR channel and on blockade of the pore by open-channel blockers.
Collapse
Affiliation(s)
- N A McCarty
- Department of Physiology, Emory University School of Medicine, Atlanta, GA 30322-3110, USA.
| |
Collapse
|
112
|
Marshall WS, Bryson SE, Luby T. Control of epithelial Cl(−) secretion by basolateral osmolality in the euryhaline teleost Fundulus heteroclitus. J Exp Biol 2000; 203:1897-905. [PMID: 10821746 DOI: 10.1242/jeb.203.12.1897] [Citation(s) in RCA: 37] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/21/2022]
Abstract
Euryhaline teleost fish adapt rapidly to salinity change and reduce their rate of ion secretion on entry to fresh water. Killifish (Fundulus heteroclitus) transferred from full-strength sea water to fresh water showed large reductions in plasma [Na(+)] and osmolality at 6 h which were corrected by 24 h. To mimic this in vitro, a hypotonic shock of 20–70 mosmol kg(−)(1) was applied on the basolateral side of opercular epithelia. This hypotonic shock reversibly reduced the short-circuit current (I(sc), equivalent to the rate of secretion of Cl(−)) in a dose-dependent fashion, with a 40 mosmol kg(−)(1) hypotonic shock reducing I(sc) by 58+/−4.6 % in 40 min. Similar reductions in [NaCl], but with added mannitol to maintain osmolality, were without effect, indicating that the effect was purely osmotic. Hypotonic inhibition of I(sc) was accompanied by reductions in epithelial conductance (G(t)) but no significant change in transepithelial potential (V(t)). The hypotonic inhibition was apparently not Ca(2+)-mediated because Ca(2+)-depleted salines, thapsigargin and ionomycin all failed to block the reduction in I(sc) produced by hypotonic shock. The inhibition was not mediated via a reduction in intracellular cyclic AMP level because cyclic AMP levels, measured by radioimmunoassay, were unchanged by hypotonic shock and by 1.0 micromol l(−)(1) clonidine (which inhibits I(sc) by changing intracellular [Ca(2+)]) but were increased markedly by 1.0 micromol l(−)(1) isoproterenol, a positive control. The protein tyrosine kinase inhibitor genistein (100 micromol l(−)(1)), but not its inactive analogue daidzein, inhibited I(sc) in normal osmolality but produced a stimulation of I(sc) after hypotonic shock (and after clonidine treatment). The inhibitory effects of genistein and hypotonicity were not additive, suggesting that the same portion of the I(sc) was inhibited by both treatments. These data are consistent with a model for Cl(−) transport regulation involving tyrosine phosphorylation in cell-swelling-induced inhibition of Cl(−) secretion when euryhaline teleosts adapt to fresh water.
Collapse
Affiliation(s)
- W S Marshall
- Department of Biology, St Francis Xavier University, Antigonish, Nova Scotia, Canada.
| | | | | |
Collapse
|
113
|
Lin LY, Weng CF, Hwang PP. Effects of cortisol and salinity challenge on water balance in developing larvae of tilapia (Oreochromis mossambicus). Physiol Biochem Zool 2000; 73:283-9. [PMID: 10893167 DOI: 10.1086/316747] [Citation(s) in RCA: 21] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 02/22/2000] [Indexed: 11/03/2022]
Abstract
Effects of exogenous cortisol on drinking rate and water content in developing larvae of tilapia (Oreochromis mossambicus) were examined. Both freshwater- and seawater-adapted larvae showed increases in drinking rates with development. Drinking rates of seawater-adapted larvae were about four- to ninefold higher than those of freshwater-adapted larvae from day 2 to day 5 after hatching. Seawater-adapted larvae showed declines in drinking rate and water content at 4 and 14 h, respectively, after immersion in 10 mg L(-1) cortisol. In the case of freshwater-adapted larvae, the drinking rate decreased after 8 h of cortisol immersion, while the water content did not show a significant change even after 32 h of cortisol immersion. In a subsequent experiment of transfer from freshwater to 20 ppt (parts per thousand, salinity) seawater, immersion in 10 mg L(-1) cortisol for 8-24 h enhanced the drinking rate in larvae at 4 h after transfer, but no significant difference was found in water contents between cortisol-treated and control groups following transfer. These results suggest that cortisol is involved in the regulation of drinking activity in developing tilapia larvae.
Collapse
Affiliation(s)
- L Y Lin
- Institute of Fisheries Science, National Taiwan University, Taipei, Taiwan, Republic of China
| | | | | |
Collapse
|
114
|
Bard SM. Multixenobiotic resistance as a cellular defense mechanism in aquatic organisms. AQUATIC TOXICOLOGY (AMSTERDAM, NETHERLANDS) 2000; 48:357-389. [PMID: 10794825 DOI: 10.1016/s0166-445x(00)00088-6] [Citation(s) in RCA: 276] [Impact Index Per Article: 11.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/23/2023]
Abstract
Multixenobiotic resistance in aquatic organisms exposed to natural toxins or anthropogenic contaminants is a phenomenon analogous to multidrug resistance in mammalian tumor cell lines tolerant of anti-cancer drugs. Multidrug resistance is commonly due to the elevated expression of transmembrane P-glycoproteins (P-gp) which actively transport a wide variety of structurally and functionally diverse compounds. The purpose of this review is to place aquatic ecotoxicological data in context of the larger multidrug resistance field of study. Information on P-glycoproteins structure, mechanism of transport, and substrate specificity gained through traditional mammalian and cell culture models is examined in conjunction with recent work on aquatic species exposed to xenobiotics both in the field and in the laboratory. The physiological function of P-glycoproteins is explored through studies of gene knockout models and expression patterns in normal tissues and tumors. The effect of xenobiotic exposures on P-gp activity and protein titer is examined in wild and captive populations of aquatic invertebrates and vertebrates. Substrate overlap and evidence of co-expression of phase I detoxification enzymes (e.g. cytochromes P450) and P-gp are presented. The role of P-gp chemosensitizers as environmental pollutants and the ecotoxicological consequences of P-gp inhibition are highlighted. The overwhelming evidence suggests that P-glycoproteins provide aquatic organisms with resistance to a wide range of natural and anthropogenic toxins.
Collapse
Affiliation(s)
- SM Bard
- Biology Department, Mail Stop #32, Woods Hole Oceanographic Institution, Woods Hole, MA, USA
| |
Collapse
|
115
|
Baudouin-Legros M, Brouillard F, Cougnon M, Tondelier D, Leclerc T, Edelman A. Modulation of CFTR gene expression in HT-29 cells by extracellular hyperosmolarity. Am J Physiol Cell Physiol 2000; 278:C49-56. [PMID: 10644511 DOI: 10.1152/ajpcell.2000.278.1.c49] [Citation(s) in RCA: 22] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
Hypertonicity has pleiotropic effects on cell function, including activation of transporters and regulation of gene expression. It is important to investigate the action of hypertonicity on cystic fibrosis gene expression because cystic fibrosis transmembrane conductance regulator (CFTR), the cAMP-regulated Cl(-) channel, regulates ion transport across the secretory epithelia, which are often in a hypertonic environment. We found that adding >150 mosmol/l NaCl, urea, or mannitol to the culture medium reduced the amount of CFTR mRNA in colon-derived HT-29 cells in a time-dependent manner. Studies with inhibitors of various kinases [H-89 (protein kinase A inhibitor), bisindolylmaleimide (protein kinase C inhibitor), staurosporine (serine/threonine kinase inhibitor) and herbimycin A (tyrosine kinase inhibitor), SB-203580 and PD-098059 (mitogen-activated protein kinase inhibitors)] showed that CFTR gene expression and its decrease by added NaCl required p38 kinase cascade activity. The CFTR gene activity is regulated at the transcriptional level, since adding NaCl diminished the luciferase activity of HeLa cells transiently transfected with the CFTR promoter. This regulation requires protein synthesis. The complexity of the reactions involved in blocking CFTR gene transcription by NaCl strongly suggests that the decrease in CFTR mRNA is part of a general cell response to hyperosmolar stress.
Collapse
Affiliation(s)
- M Baudouin-Legros
- Institut National de la Santé et de la Recherche Médicale Unité 467, Faculté de Médecine Necker-Enfants Malades, 75015 Paris, France.
| | | | | | | | | | | |
Collapse
|
116
|
|
117
|
Marshall WS, Emberley TR, Singer TD, Bryson SE, Mccormick SD. Time course of salinity adaptation in a strongly euryhaline estuarine teleost, fundulus heteroclitus: a multivariable approach. J Exp Biol 1999; 202 (Pt 11):1535-44. [PMID: 10229699 DOI: 10.1242/jeb.202.11.1535] [Citation(s) in RCA: 135] [Impact Index Per Article: 5.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Abstract
Freshwater-adapted killifish (Fundulus heteroclitus) were transferred directly from soft fresh water to full-strength sea water for periods of 1 h, 3 h, 8 h and 1, 2, 7, 14 and 30 days. Controls were transferred to fresh water for 24 h. Measured variables included: blood [Na+], osmolality, glucose and cortisol levels, basal and stimulated rates of ion transport and permeability of in vitro opercular epithelium, gill Na+/K+-ATPase and citrate synthase activity and chloride cell ultrastructure. These data were compared with previously published killifish cystic fibrosis transmembrane conductance regulator (kfCFTR) expression in the gills measured over a similar time course. Plasma cortisol levels peaked at 1 h, coincident with a rise in plasma [Na+]. At 8 h after transfer to sea water, a time at which previous work has shown kfCFTR expression to be elevated, blood osmolality and [Na+] were high, and cortisol levels and opercular membrane short-circuit current (Isc; a measure of Cl- secretion rate) were low. The 24 h group, which showed the highest level of kfCFTR expression, had the highest plasma [Na+] and osmolality, elevated plasma cortisol levels, significantly lower opercular membrane resistance, an increased opercular membrane ion secretion rate and collapsed tubule inclusions in mitochondria-rich cells, but no change in gill Na+/K+-ATPase and citrate synthase activity or plasma glucose levels. Apparently, killifish have a rapid (<1 h) cortisol response to salinity coupled to subsequent (8–48 h) expression of kfCFTR anion channel proteins in existing mitochondria-rich cells that convert transport from ion uptake to ion secretion.
Collapse
Affiliation(s)
- WS Marshall
- Department of Biology, St Francis Xavier University, Antigonish, Nova Scotia, Canada B2G 2W5, Vanderbilt University, Department of Anaesthesiology, Laboratory of Cellular and Molecular Physiology, 1313 21st Avenue South, Nashville, TN 37232-21
| | | | | | | | | |
Collapse
|