Taurine transport by isolated flounder renal tubules

Journal of Comparative Physiology B, 1985

Taurine transport was investigated in brush border membrane vesicles isolated from renal tubules of the winter flounder (Pseudopleuronectes americanus). Taurine uptake by the vesicles was greater in the presence of NaC1 as compared to uptake in KC1. The Na+-dependent taurine transport was electrogenic and demonstrated tracer replacement and inhibition by fl-alanine and HgCI2, indicating the presence of Na +-dependent, carrier-mediated taurine transport. In contrast to Na+-dependent taurine transport across the basolateral membrane, there was not a specific C1-dependency for transport in the brush border membrane. No evidence was obtained for Na+-independent carrier-mediated taurine transport. The possible involvement of the brush border Na+-dependent transport system in the net secretion of taurine from blood to tubular lumen in vivo (Schrock et al. 1982) is discussed.

Journal of Experimental Zoology, 1986

Taurine transport by the flounder gut was characterized in isolated strips of intestine mounted between Ringer's solutions. Taurine was transported into the cell, against its concentration gradient, by a sodiumdependent system present in both the mucosal and serosal membranes. This system appears to be specific for p-amino acids and is regulated by cyclic nucleotides (cGMP and CAMP). Kinetic analyses indicated that under physiological conditions the magnitudes of the bidirectional taurine uptake rates would favor net absorption of taurine from lumen to blood.

Journal of Experimental Biology

95% of the Na(+)-independent influx of taurine in flounder erythrocytes at normal osmolality (330 mosmol kg-1) and 0.30 mmol l-1 taurine was mediated by a saturable system (Vmax = 0.689 nmol g-1 dry mass min-1; Km = 0.47 mmol l-1). The influx was inhibited by taurine analogues, but was not significantly affected by reduced osmolality. This saturable influx of taurine was probably mediated by the so-called Na(+)-dependent influx system for taurine operating in the 0 Na+: 1 taurine mode. The remaining 5% of the Na(+)-independent influx was mediated by a diffusional pathway (Kd = 0.050 microliter g-1 dry mass min-1), since it did not show saturation kinetics, was not inhibited by taurine analogues and did not mediate counter-exchange. This non-saturable influx system for taurine was strongly, but transiently, stimulated by reduction of osmolality. The time course for this stimulatory effect was the same as that for the system that mediates the volume regulatory efflux of taurine. The r...

Amino Acids, 2012

Flatfish species seem to require dietary taurine for normal growth and development. Although dietary taurine supplementation has been recommended for flatfish, little is known about the mechanisms of taurine absorption in the digestive tract of flatfish throughout ontogeny. This study described the cloning and ontogenetic expression of the taurine transporter (TauT) in the flatfish Senegalese sole (Solea senegalensis). Results showed a high similarity between TauT in Senegalese sole and other vertebrates, but a change in TauT amino acid sequences indicates that taurine transport may differ between mammals and fish, reptiles or birds. Moreover, results showed that Senegalese sole metamorphosis is an important developmental trigger to promote taurine transport in larvae, especially in muscle tissues, which may be important for larval growth. Results also indicated that the capacity to uptake dietary taurine in the digestive tract is already established in larvae at the onset of metamorphosis. In Senegalese sole juveniles, TauT expression was highest in brain, heart and eye. These are organs where taurine is usually found in high concentrations and is believed to play important biological roles. In the digestive tract of juveniles, TauT was more expressed in stomach and hindgut, indicating that dietary taurine is quickly absorbed when digestion begins and taurine endogenously used for bile salt conjugation may be recycled at the posterior end of the digestive tract. Therefore, these results suggest an enterohepatic recycling pathway for taurine in Senegalese sole, a process that may be important for maintenance of the taurine body levels in flatfish species.

The Journal of Physiology, 1986

1. The taurine transport of flounder erythrocytes is associated with a cell volume regulation in anisosmotic media. An osmolality reduction leads to a cell volume increase, which is followed by a volume readjustment towards the original level. A 75 mosm reduction is accompanied by a 33 ,mol g dry wt.-' reduction in the cellular taurine content. 2. The reduction in osmolality activates the taurine release mechanism by transiently increasing the rate coefficient for taurine efflux. The rate coefficient for taurine influx is similarly stimulated. This influx is mediated by a Na+-independent transport system. The concomitant activation of influx and efflux suggests a coupling between these two systems. 3. Higher taurine efflux and influx rate coefficients which decayed more slowly with time were measured in cells suspended in Na+-free (choline replacement) media than in the presence of Na+. This suggests that Na+ may play a role in the taurine release mechanism. 4. Noradrenaline induced a cellular swelling at normal osmolality (330 mosm), but had only a minor effect on the taurine efflux and influx and the cellular taurine content. 5. Urea-induced cellular swelling at normal osmolality initiated a volume regulatory process and activated the taurine release mechanism, similarly to an osmolality reduction. 6. These results show that osmolality reduction and cellular swelling are no prerequisites for the activation of the taurine release mechanism and the cell volume readjustment. 7. It is suggested that the dimension of an intracellular solute compartment determines the activation level of this mechanism. * The order of names is alphabetical.

Journal of Experimental Biology

The exchange of taurine across epidermal epithelia of Mytilus edulis and M. californianus was studied U9ing radiotracer and chromatographic (HPLC) methods. Gill levels of taurine in both species ranged from 60 to 70μmolg−1 wet weight. Net uptake of taurine, determined using HPLC, occurred down to ambient concentrations as low as 10 nmol−1. The rate of taurine loss from mussels was about 0.02/μmolg−1 wet body weighth−1, and when exposed to amino-acid-free sea water, external taurine concentration increased until a steady-state of about 15 nmoll−1 was achieved. Mussels accumulated inhibitors of taurine transport at rates which were directly related to their relative inhibitory capacities: β-alanine >β-aminobutyric acid ⋍ γ-aminobutyric acid (GABA). Addition of large concentrations (50–200 μmol−1) of GABA resulted in a rapid increase in taurine concentration in test solutions. This increase was consistent with a model in which GABA both competitively inhibits the reaccumulation of e...

Marine drugs, 2017

Although taurine has been shown to play multiple important physiological roles in teleosts, little is known about the molecular mechanisms underlying dietary requirements. Cell lines can provide useful tools for deciphering biosynthetic pathways and their regulation. However, culture media and sera contain variable taurine levels. To provide a useful cell line for the investigation of taurine homeostasis, an adult zebrafish liver cell line (ZFL) has been adapted to a taurine-free medium by gradual accommodation to a commercially available synthetic medium, UltraMEM™-ITES. Here we show that ZFL cells are able to synthesize taurine and be maintained in medium without taurine. This has allowed for the investigation of the effects of taurine supplementation on cell growth, cellular amino acid pools, as well as the expression of the taurine biosynthetic pathway and taurine transporter genes in a defined fish cell type. After taurine supplementation, cellular taurine levels increase but h...

Proceedings of the National Academy of Sciences, India Section B: Biological Sciences, 2019

The present study investigated the role of taurine in cellular volume regulation of erythrocytes isolated from freshwater air-breathing magur catfish (Clarias magur) under osmotic stress. Exposure of erythrocytes, pre-loaded with or without taurine, to hypotonic medium (-80 mOsmol/L) led to a significant decrease in taurine level in the erythrocytes due to efflux of taurine through a band 3 transporter protein present in the plasma membrane with a slight increase in cellular volume of erythrocytes by 12-13%, whereas incubation of erythrocytes with hypertonic medium (? 80 mOsmol/L) with taurine caused a significant uptake of taurine by the erythrocytes through the Na ?-dependent pathway but without any loss of taurine from the erythrocytes which was accompanied by a slight decrease in the cellular volume of erythrocytes by 11-12%. Furthermore, a direct correlation between the osmosensitive cellular volume and taurine release could be established in the erythrocytes of magur catfish under hypotonic stress (r = 0.9921). In conclusion, the erythrocytes of airbreathing magur catfish do possess a very efficient taurinedependent volume regulatory mechanism to resist the changes in cellular volume under anisotonic conditions as a unique adaptational strategy to defend against the osmosensitive changes in cellular volume of erythrocytes.

Biochimica et Biophysica Acta (BBA) - Biomembranes, 1991

The uptake of famine by luminal membrane vesicles from pars eonvoluta and pars recta o! rabbit proximal tubule was examined. In pars convolnta, the transport of taudne was characterized by two Na+-dependent (Kml = 0.086 raM, Kin2 = 5.41 raM) systems, and one Na+-independent (K a = 2.~ ~'] mM) system, which hi the presence of an inwardly dh~ctnd H +-gradient was able to drive the transport of {aurine into these vesicles. By contrast, in luminal membrane vesicles from pars recta, the transport of taurine occurred via a dual transport system (Kmt-~ 0.012 mM, K=z = 5.62 raM), which was strictly dependent on Na +. At acidic pH with or without a H +-gradient, the Na+-depandant flux off {auriae was drastically reduced. In both kind of vesicles, competition experiments only showed inhibition of the Na+-dependant high-affinity {amine transporter in the presence of ~'.alanine, whereas there was no significant inhibition with a-amino acids, indicating a fl-amino acid specific transport system. Addition of fl-alanine, L-alanine, L-proline mul glyeine, hut not L-serine reduced the H +-dependent uptake of famine to approx. 50%. Moreover, only the Na+-dependent high-affinity transport systems in both segments specifically required CI-. Investigation of the stnlehlomet~ indicated 1.8 Na + : l el-: 1 famine (high affinity), I Na+: I taurine 0ow affinity) and I n +: I taurine in pars convolu{a. In pars recta, the data shewed 1.8 Na+:l CI-:I {aurine (high afrmity) and 1 Na+:l {amine (low affinity).

Comparative Biochemistry and Physiology Part A: Physiology, 1980

The effect of Na+ and osmolality on influx of taurine and GABA, and steady state distribution of Na+, K+, Cl-, taurine and GABA, has been measured in flounder (Platichrhys jesus) erythrocytes. 2. A reduction in osmolality only, lead to a net release of taurine, GABA, K+ and Cl-during the restoration of normal volume. 3. Taurine and GABA influx was Na-dependent, a minor fraction was Na-independent. 4. A reduced osmolality stimulated taurine influx. 5. Present work supports the hypothesis that flounder erythrocyte taurine and GABA concentrations are controlled by factors correlated to plasma osmolality.