Taurine transport systems in the ciliate protozoanTetrahymena pyriformis |
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Authors: | B Kramhøft Dr I H Lambert |
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Institution: | (1) August Krogh Institute, Biochemical Department, 13, Universitetsparken, DK-2100 Copenhagen Ø, Denmark;(2) Present address: Carlsberg Laboratory, Chemical Department GL., Carlsbergvej 10, DK-2500 Jalby |
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Abstract: | Summary
Tetrahymena pyriformis cultivated in the presence of 1 mM taurine prior to transfer of the cells to non-nutrient medium express an enhanced capacity for concentrative taurine uptake and for taurine diffusion compared to cells grown without added taurine. The unidirectional taurine influx in taurine-grown cells comprises a saturable component with Km -257M, Vmax = 21 n-moles · g dry wt–1 sd min–1, and a diffusion component with a diffusion constant of 0.20 ml · g dry wt–1 · min–1. At extracellular taurine concentrations <30M, 20% of the influx is via the saturable system and 80% is via the diffusion system. 19% of the influx in Na+-dependent, Cl–-independent, and not inhibitable with structural analogues to taurine, suggesting that the transport system responsible for the saturable component in Tetrahymena is different from the Na+- and Cl–-dependent taurine translocating system (the-system) described in vertebrate cells. The unidirectional taurine influx is reduced by 80% by 1mM DIDS (inhibitor of anion exchange and anion channels) and by 1 mM MK196 (indachrinone, inhibitor of anion channels) indicating that taurine diffusion inTetrahymena is via a channel, which is permanently active and which resembles the swelling-induced taurine channel seen in mammalian cells. Taurine influx is stimulated by the forskolin analogue 1,9-dideoxyforskolin and by arachidonic acid, and this stimulation is in both cases sensitive to DIDS and MK196.Abbreviations DDF
dideoxyforskolin
- DIDS
4,4-diisothiocyano-2,2-stilbene disulfonic acid
- GABA
gamma amino butyric acid
- HEPES
N(2-hydroxyethyl)piperazine-N-(2-ethane sulfonic acid)
- MK196
indachrinone
- MOPS
3-(N-morpholino)propane sulfonic acid
- NMDG
n-methyl-dglucamonium
- OPA
ortho-phtalaldehyde
- PCA
perchloric acid
- TES
N-tris(hydroxy methyl)-methyl-2-amino ethane sulfonic acid
- TRIS
tris(hydroxy methyl)amino methane |
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Keywords: | Amino acids Taurine channels Arachidonic acid DIDS -1 9-Dideoxyforskolin Indachrinone |
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