1887

Abstract

Summary: The effect of medium hypo-osmolality on cell volume and intracellular amino acid composition was studied in the protozoan parasite . When was exposed to hypotonic medium, it initially swelled by 40% of its original volume and then decreased its volume, thus demonstrating a regulatory volume decrease process (RVD). These processes were accompanied by a rapid release of intracellular neutral amino acids, especially alanine, but not by amino acids with net charges such as glutamate and ornithine. The net alanine efflux was Na and Cl independent, and sensitive to medium osmolality. Alanine efflux was sigmoidal with respect to medium osmolality, with an approximately linear relationship over a range of 250 mOsm kg. Alanine efflux was also sensitive to temperature, and an Arrhenius plot gave a of 3.6 and an activation energy of 25 kcal mol (105 kJ mol), suggesting that a carrier-type transport protein, or uniport, was involved in the net alanine efflux under hypotonic conditions. This volume-activated (VA) alanine efflux was not inhibited by ionophores or chloride channel blockers. Of the potential inhibitors tested, only -hydroxymercuribenzoate inhibited net alanine efflux. This thiol reagent also inhibited giardial RVD, suggesting that alanine efflux plays a significant role in this process. The VA (alanine) uniport was able to transport 2-aminoisobutyric acid (AIB), a structural analogue of alanine which is frequently used for the characterization of eukaryotic alanine transport, but which is not transported by under isotonic conditions. On the basis of AIB uptake under hypotonic conditions and lack of transactivation of AIB efflux from AIB-loaded cells by external 10 mM alanine or glycine under isotonic conditions, it is evident that the VA (alanine) uniport is different from the previously reported (alanine) antiport.

Loading

Article metrics loading...

/content/journal/micro/10.1099/13500872-141-10-2455
1995-10-01
2024-05-09
Loading full text...

Full text loading...

/deliver/fulltext/micro/141/10/mic-141-10-2455.html?itemId=/content/journal/micro/10.1099/13500872-141-10-2455&mimeType=html&fmt=ahah

References

  1. Briones M.R.S., Nelson K., Beverley S.M., Affonso H.T., Camargo E.P., Floeter-Winter L.M. 1992; Leishmania tarentolae taxonomic relatedness from phylogenic analysis of the small subunit ribosomal RNA gene.. Mol Biochem Parasitol 53:121–128
    [Google Scholar]
  2. Chamberlin M.E., Strange K. 1989; Anisosmotic cell volume regulation: a comparative view.. Am J Physiol 257:Cl59–C173
    [Google Scholar]
  3. Darling T.N., Burrows C.M., Blum J.J. 1990; Rapid shape change and release of ninhydrin-positive substances by Leishmania major promastigotes in response to hypo-osmotic stress.. J Protocol 37:493–499
    [Google Scholar]
  4. Edwards M.R., Gilroy F.V., Jimenez B.M., O’Sullivan W.J. 1989; Alanine is a major end product of metabolism of Giardia lamblia: proton nuclear magnetic resonance study.. Mol Biochem Parasitol 37:19–26
    [Google Scholar]
  5. Edwards M.R., Knodler L.A., Wilson J.R., Schofield P.J. 1993; The transport and metabolism of alanine by Giardia intestinalis. . Mol Biochem Parasitol 61:49–58
    [Google Scholar]
  6. Fincham D.A., Wolowyk M.W., Young J.D. 1987; Volume- sensitive taurine transport in fish erythrocytes.. J Membrane Biol 96:45–56
    [Google Scholar]
  7. Gilles R. 1987; Volume regulation in cells of euryhaline invertebrate.. In Cell Volume Control: Fundamental and Comparative Aspects in Animal Cells pp. 205–247 Edited by Gilles R., Kleinzeller A., Bolis L. New York: Academic Press;
    [Google Scholar]
  8. Goldstein L., Brill S.R. 1991; Volume-activated taurine efflux from skate erythrocytes: possible band 3 involvement.. Am J Physiol 260:R1014–R1020
    [Google Scholar]
  9. Haynes J.K., Goldstein L. 1993; Volume-regulatory amino acid transport in erythrocytes of the little skate, Raja erinacea. . Am J Physiol 265:R173–R179
    [Google Scholar]
  10. Hoffmann E.K., Lambert I.H. 1983; Amino acid transport and cell volume regulation in Ehrlich ascites tumour cells.. J Physiol 338:613–625
    [Google Scholar]
  11. Huxtable R.J. 1992; Physiological actions of taurine.. Physiol Rev 72:101–163
    [Google Scholar]
  12. Kirk K., Ellory J.C., Young j.D. 1992; Transport of organic substrates via a volume-activated channel.. J Biol Chem 267:23475–23478
    [Google Scholar]
  13. Knodler L.A., Edwards M.R., Schofield P.J. 1994; The intracellular amino acid pools of Giardia intestinalis, Trichomonas vaginalis and Crithidia luciliae. . Exp Parasitol 79:117–125
    [Google Scholar]
  14. Lenaers G., Nielsen H., Engberg J., Herzog M. 1988; The secondary structure of large-subunit rRNA divergent domains, a marker for protist evolution.. Biosystems 21:215–222
    [Google Scholar]
  15. Lepley P.R., Mukkada A.J. 1983; Characteristics of an uptake system for a-aminoisobutyric acid in Leishmania tropica promastigotes.. J Protocol 30:41–46
    [Google Scholar]
  16. Moyes C.D., Moon T.W., Ballantyne J.S. 1986; Osmotic effects on amino acid oxidation in skate liver mitochondria.. J Exp Biol 125:181–195
    [Google Scholar]
  17. Nygaard T., Bennett C.C., Grossman G., Edwards M.R., Schofield P.J. 1994; Efflux of alanine by Giardia intestinalis. . Mol Biochem Parasitol 64:145–152
    [Google Scholar]
  18. Padan E., Zilberstein D., Rottenberg H. 1976; The proton electrochemical gradient in Escherichia coli cells.. Eur J Biochem 63:533–541
    [Google Scholar]
  19. Schofield P.J., Edwards M.R., Matthews J., Wilson J.R. 1992; The pathway of arginine catabolism in Giardia intestinalis. . Mol Biochem Parasitol 51:29–36
    [Google Scholar]
  20. Shotwell M.A., Oxender D.L. 1983; The regulation of neutral amino acid transport by amino acid availability in animal cells.. Trends Biochem Sci 8:314–316
    [Google Scholar]
  21. Sogin M.L, Elwood H.J., Alonso R.A., Peattie D.A. 1989; Phylogenic meaning of the kingdom concept: an unusual ribosomal RNA from Giardia lamblia. . Science 243:75–77
    [Google Scholar]
http://instance.metastore.ingenta.com/content/journal/micro/10.1099/13500872-141-10-2455
Loading
/content/journal/micro/10.1099/13500872-141-10-2455
Loading

Data & Media loading...

This is a required field
Please enter a valid email address
Approval was a Success
Invalid data
An Error Occurred
Approval was partially successful, following selected items could not be processed due to error