Role of taurine in osmoregulation during endurance exercise

Abstract

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.

Expression and functional analysis of mussel taurine transporter, as a key molecule in cellular osmoconforming

“…The mussel mainly utilizes taurine as an osmolyte, as described above, and therefore, taurine is accumulated at a high concentration in the mussel cells. Taurine in hemolymph is also highly concentrated, for example, in the common mussel, taurine concentration in the hemolymph is approximately 500·mol·l -1 (Zurburg and DeZwaan, 1981), which is one order of magnitude higher than that in mammals (approximately 50-80·mol·l -1 in plasma; Cuisinier et al, 2002;Delaney et al, 2003;Pacioretty et al, 2001). In addition, taurine is dominant and accounts for approximately 80% of the total amino acid pool in the mussel (Toyohara and Hosoi, 2004), suggesting that the concentration and proportion of taurine is much higher than in mammals.…”

Exercise-induced changes in amino acid levels in skeletal muscle and plasma

“…Cuisinier et al 76) examined the relationship between plasma taurine levels and osmolality in subjects who had undergone a 90-min cycle exercise under a hydrated or dehydrated condition. They found significant increases in osmolality only under the dehydrated condition, and increases in plasma taurine levels along with an extension of exercise time under the dehydrated condition.…”

“…Prolonged exercise may damage membranes in a wider area, leading to activation of immune cells 73,74) . The hypothesis proposed was that such activated immune cells in dam-regulatory action 76) and antioxidative effect 81) of taurine, even before exercise, might suppress taurine release into the plasma 80) . It is therefore likely that taurine is released from muscles into the bloodstream upon exercise-induced stimulation, such as the production of reactive oxygen species and anoxia; and plasma taurine is involved in the osmoregulation and antioxidant action.…”

Effects of taurine administration on exercise-induced fatigue and recovery

“…In humans, a significant change in the taurine level in skeletal muscle has not been observed in resistance 7) or endurance 2,4-6) exercises because (at least in part) of large individual differences in dietary intakes of taurine and precursors of taurine synthesis such as methionine and cysteine. The taurine level in blood is increased by prolonged exercise 12) , so it can be assumed that taurine is released from tissues by endurance exercise. Based on the observation that the taurine concentration in blood during endurance exercise is higher in the dehydrated condition than that in the hydrated condition 12) , an increased taurine level in blood due to exercise seems to be related to osmoregulation in tissues.…”

“…In human skeletal muscle, taurine content is higher than that of glutamine, which is the most abundant amino acid [4][5][6][7] . The taurine concentration in plasma is around 10-100 μM in humans 12) and μM in mice and rats [8][9][10][11] . Taurine is taken up by tissues through a taurine transporter (TAUT), which belongs to a family of Na + /Cl − -dependent neurotransmitter transporters.…”