Taurine In Osmoregulation Research Articles

Comparison of the carnosine and taurine contents of vastus lateralis of elderly Korean males, with impaired glucose tolerance, and young elite Korean swimmers

The carnosine and taurine contents of the vastus lateralis of two diverse groups of Korean male subjects (elderly and impaired glucose-tolerant (IGT) subjects and young elite swimmers at a national sport university) having a similar national diet, were examined. Despite marked differences in age, fitness and clinical status the two groups showed almost identical muscle carnosine and taurine contents. In the case of carnosine, the results suggest a similar contribution to intracellular buffering capacity in the two groups of subjects, with no evidence of a reduction of this in elderly IGT subjects. In addition, both groups showed the same inverse relationship between the muscle carnosine and taurine contents; the spread of values between subjects, within-groups, most likely reflect variations in the type I (low carnosine, high taurine) or type II (high carnosine, low taurine) composition of the vastus lateralis. The relationship is consistent with a role of taurine in osmoregulation, compensating for variations between fibre types in the carnosine content.

Role of taurine in osmoregulation during endurance exercise.

Taurine is released by contracting muscles, but its actual role remains unspecified. In this study, we investigated whether the exercise-stimulated release of taurine from muscle into the plasma regulates the modification of osmolality induced by intramuscular osmolyte production. Six subjects performed 90 min of cycling exercise (at 70% maximum power output) on two occasions, with (HC) or without (DC) fluid intake. Taurine content was determined in plasma, blood cells and urine before and after the endurance events, together with plasma osmolality. Plasma osmolality increased by 4% in the DC experiment ( P<0.01), but remained stable in the HC condition. The exercise also induced changes in the mean (SD) plasma taurine content to a greater degree in HC [+63 (26)%] than in DC [+33 (18)%; P<0.05], supporting the hypothesis that taurine is released into the plasma via an osmoregulatory process. However, the higher plasma taurine content in HC was not related to changes in renal taurine. In addition, the increase of taurine in plasma was not related to its release from blood cells since their taurine concentration increased by 70% both in HC [429 (77) to 680 (82) microM; P=0.003] and in DC [451 (57) to 731 (34) microM; P<0.001]. The lack of correlation between plasma volume modification and the mass ratio of taurine would exclude a major role for taurine exchange in plasma volume regulation. Sodium ( R=0.967, P<0.001), chloride ( R=0.917, P<0.001) and osmolality ( R=0.924, P<0.001) seem to be the main regulators of plasma volume changes during exercise. In conclusion, changes in the plasma taurine content during endurance exercise is related to an osmoregulatory process, but this alone does not control plasma volume changes.

Evidence that taurine modulates osmoregulation by modification of osmolarity sensor protein ENVZ ? expression

Although the involvement of taurine in osmoregulation is well-documented and widely accepted, no detailed mechanism for this function has been reported so far. We used subtractive hybridization to study mRNA steady state levels of genes up- or downregulated by taurine. Rats were fed taurine 100 mg/kg body weight per day for a period of three days and hearts (total ventricular tissue) of experimental animals and controls were pooled and used for mRNA extraction. mRNAs from two groups were used for subtractive hybridization. Clones of the subtractive library were sequenced and the obtained sequences were identified by gen bank assignment. Two clones were found to contain sequences which could be assigned to the osmolarity sensor protein envZ, showing homologies of 61 and 65%. EnvZ is an inner membrane protein in bacteria, important for osmosensing and required for porine gene regulation. It undergoes autophosphorylation and subsequently phosphorylates OmpR, which in turn binds to the porine (outer membrane protein) promoters to regulate the expression of OmpF and OmpC, major outer membrane porines. This is the first report of an osmosensing mechanism in the mammalian system, which was described in bacteria only. Furthermore, we are assigning a tentative role for taurine in the osmoregulatory process by modifying the expression of the osmoregulatory sensor protein ENVZ.

Role of taurine in osmoregulation in brain cells: Mechanisms and functional implications

All cells including neurons and glial cells are able to keep their volume within a very limited range. The volume regulatory mechanism involves changes in the concentration of osmolytes of which taurine appears to be of particular importance in brain cells. Swelling in brain cells may occur as a result of depolarization or small fluctuations in osmolarity. In isolated brain cells these conditions will always lead to a release of taurine, the time course of which is superimposable on that of the volume regulatory decrease which follows the initial cell swelling. The mechanism responsible for taurine release associated with swelling has not been fully elucidated but a large body of evidence seems to exclude participation of the taurme high affinity carrier. Using a number of inhibitors of anion exchangers it has been demonstrated that both volume regulation and taurine release in brain cells are inhibited by these drugs, implicating an anion channel in the process. It has be controversial issue as to whether or not taurine release is Ca++ dependent. Recent evidence appears to suggest that the release process is not associated with Ca++ or Ca++ channels. It is, however, quite possible that the swelling process may involve the Ca++ calmodulin system or other second messengers. Taurine also contributes to volume regulation after shrinkage of brain cells, in this case by increasing its intracellular concentration. This change is accomplished byan upregulation of the Na+/taurine cotransporter, together with reduced passive fluxes and increased endogenous synthesis.

Ultrastructural localization of taurine immunoreactivity in the pineal organ and retina of the pigeon.

While taurine is ubiquitous in animal tissues, some of the highest levels occur in the hypothalamus, pituitary gland, retina and pineal organ3, 11, 13. This may indicate a role of taurine in processes that are more pronounced in neurosecretory and neurosensory cells than in other cell types. For example, taurine has been shown to interact with membrane phospholipids to alter their Ca2+ binding properties7, and may thus influence Ca2+-dependent processes such as ATPase ion pumps, ion channels flux, or Ca2+-activated events5, 6, many of which contribute to neurosecretion and phototransduction. On the other hand, the large transient ionic fluxes associated with activity of pineal and retinal neurosensory/neurosecretory cells may also impose osmotic stresses that require use of taurine as an osmolyte; there is much evidence concerning a role for taurine in osmoregulation in tissues ranging from marine organisms, to the kidney and the brain5, 6. The pineal organ contains many structures homologous to retinal photoreceptors. We hoped to gain information about the role of taurine in these tissues by examining and comparing the retinal and pineal distribution of endogenous taurine using immunocytochemistry.KeywordsPineal GlandSmooth Endoplasmic ReticulumElectron Microscope LevelUltrastructural LocalizationPineal OrganThese keywords were added by machine and not by the authors. This process is experimental and the keywords may be updated as the learning algorithm improves.

Taurine and Osmoregulation. III. Taurine Deficiency Protects against Cerebral Edema during Acute Hyponatremia

Taurine is a cerebral osmoprotective molecule during chronic hypernatremic dehydration. In these experiments, we investigated the role of taurine in osmoregulation during acute hyponatremia. Taurine deficiency was induced in experimental cats (n = 6) by feeding a taurine-free diet for 8-10 wk, whereas control counterparts (n = 6) consumed a regular diet. Hyponatremia was provoked in all cats over 54 h by daily injections of 5% dextrose in water (7.5% body wt) and vasopressin (20 U/d). The serum Na+ concentration was abruptly lowered to 110 +/- 3 and 117 +/- 2 mmol/L, in experimental and control animals, respectively. The cerebral total and intracellular water compartment sizes were reduced from 486 +/- 11 to 441 +/- 11 ml/100 g dry wt and from 357 +/- 7 to 309 +/- 12 mL/100 g dry wt, respectively, in control versus experimental cats, p less than 0.05. There was a significant linear relationship between cerebral taurine content and the intracellular water compartment size in all animals, p less than 0.02. Taurine displayed a similar osmoprotective capacity in muscle tissue in these studies. We conclude that taurine is an osmoregulatory molecule in cerebral and extracerebral tissues during severe hyponatremia. Reductions in tissue taurine content may complement decreases in cytosolic electrolyte levels during adaptation to more prolonged hyponatremia.

A possible role for taurine in osmoregulation within the brain.

Intracranial microdialysis was used to measure changes in extracellular amino acids within the rat brain during local osmotic alteration of the extracellular microenvironment or during systemic water intoxication. Increased cellular hydration produced by either of these methods was accompanied by a marked increase in extracellular taurine levels without affecting the other amino acids measured. With local osmotic alteration, this increase was osmolarity dependent and reversible. The specificity, sensitivity, and reversibility of the increase in extracellular taurine strongly suggest a functional role in osmoregulation in the brain under normal as well as pathological conditions.

Taurine in the osmoregulation of the Brattleboro rat

The function of taurine in mammalian osmoregulation was studied in the Brattleboro rat with hereditary hypothalamic diabetes insipidus (DI). DI rats are chronically dehydrated because of their inability to synthesize vasopressin. One day of water deprivation did not affect the water balance in rats with normal vasopressin synthesis, whereas DI rats were markedly dehydrated and lost considerably body weight. Taurine content and 3H-taurine accumulation by platelets were significantly higher in DI rats, with a further increase after one day of water deprivation. In DI rats, water deprivation also evoked a clear taurine increase in skeletal muscle and in the brain. These findings indicate that taurine has an osmoregulatory function in mammals.

The role of amino acids and taurine in isosmotic intracellular regulation in Ehrlich ascites mouse tumour cells

1. Ehrlich ascites tumour cells swollen in hypotonic medium reduce their volumes towards that found in isotonic medium. 2. This regulation of cell volume implies an adjustment of the intracellular amount of osmotically active substances, i.e. a type of “isosmotic intracellular regulation”. 3. Non-protein ninhydrin-positive substances were lost from the cells during this volume regulation. 4. Amino acid analyses show that the non-essential amino acids play a significant role in this process. 5. The relative decrease in concentration was larger for taurine than for any other measured inorganic and organic substance. The absolute change in intracellular taurine concentration is third only to changes in chloride and potassium. The role of taurine in osmoregulation is similar to that observed in many aquatic invertebrates. 6. The steady state distribution of amino acids varies with the magnitude of the Na+ and K+ concentration gradients between the cells and their environment. The ion gradient hypothesis fits our data only if we introduce a leakage pathway for the amino acids which is independent of the amino acid pump and which varies with the cell volume.