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fbtwitterlinkedinvimeoflicker grey 14rssslideshare1
Publisher: Science Reviews 2000
Languages: English
Types: Article
Subjects: bcs
1. The explanted blastoderm of the Japanese quail was used to explore the role of ions and carbon dioxide in determining the rate of sub-embryonic fluid (SEF) production between 54 and 72 h of incubation.\ud 2. Amiloride, an inhibitor of Na+/H+ exchange, at concentrations of 10-3 to 10-6 M substantially decreased the rate of SEF production when added to the albumen culture medium. N-ethylmaleimide, an inhibitor of V type H+ ATPase, also decreased this rate but only to a small extent at the highest dose applied, 10-3 M. Both inhibitors had no effect on SEF production when added to the SEF. 3. The inhibitors of cellular bicarbonate and chloride exchange, 4-acetamido-4-'isothiocyano-2, 2-'disulphonic acid (SITS) and 4,4'diisothiocyanostilbene-2,2-'disulphonic acid (DIDS), had no effect upon SEF production.\ud 4. Ouabain, an inhibitor of Na+/K+ ATPase, decreased SEF production substantially at all concentrations added to the SEF (10-3 to 10-6 M). Three sulphonamide inhibitors of carbonic anhydrase, acetazolamide, ethoxzolamide and benzolamide, decreased SEF production when added to the SEF at concentrations of 10-3 to 10-6 M. Benzolamide was by far the most potent. Neither ouabain nor the sulphonamides altered SEF production when added to the albumen culture medium.\ud 5. Using a cobalt precipitation method, carbonic anhydrase activity was localised to the endodermal cells of the area vasculosa. The carbonic anhydrase activity was primarily associated with the lateral plasma membranes, which together with the potent inhibitory effect of benzolamide, suggests the carbonic anhydrase of these cells is the membrane-associated form, CA IV.\ud 6. The changes in SEF composition produced by inhibitors were consistent with the production of SEF by local osmotic gradients.\ud 7. It is concluded that a Na+/K+ ATPase is located on the basolateral membranes of the endodermal cells of the area vasculosa , and that a sodium ion/hydrogen ion exchanger is located on their apical surfaces. Protons for this exchanger would be provided by the hydration of CO2 catalysed by the membrane-associated carbonic anhydrase. Furthermore, it is proposed that the prime function of the endodermal cells of the area vasculosa is the production of SEF.
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    • BABIKER, E.M. & BAGGOTT, G.K. (1992) Effect of turning upon the sub-embryonic fluid and albumen of the egg of the Japanese quail. British Poultry Science, 33: 973-991.
    • DIAMOND, J. (1979) Osmotic water flow in leaky epithelia. Journal of Membrane Biology, 51: 195-216.
    • DIAMOND, J.M. & BOSSERT, W.H. (1967) Standing-gradient osmotic flow. A mechanism for coupling of water and solute transport in epithelia. Journal of General Physiology, 50: 2061- 2083.
    • FRITSCHE, C., KLEINMAN, BAIN, J.L.W., HEINEN, R.R. & RILEY, D.A. (1991) Carbonic anhydrase and proton secretion in turtle bladder mitochondrial-rich cells. American Journal of Physiology, 260 : F-443-F458.
    • GREGER, R., KUNZELMANN, K. & GERLACH, L. (1990) Mechanisms of chloride transport in secretory epithelia. Annals of the New York Academy of Sciences, 574: 403-15.
    • O'GRADY S.M., MUSCH, M.W. & FIELD, M. (1990) Diuretic compounds structurally related to furosemide. Methods in Enzymology, 191: 781-792.
    • SLY, W.S. & HU, P.Y. (1995) Human carbonic anhydrases and carbonic anhydrase deficiencies. Annual Review of Biochemistry, 64: 375-401.
    • WISTRAND, P. J. & KNUUTTILA, K. G. (1989) Renal Membrane-Bound Carbonic-Anhydrase - Purification and Properties. Kidney International, 35: 851-859.
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