One of the main physiological functions of taurine in humans and animals is that of osmoregulation. Osmoregulation is pivotal to cell survival in animals and humans because the plasma membrane is permeable to many solutes and water and this creates the risk that the cell can become desiccated or undergo lysis based on the solute concentrations of the internal and external environments. Cells need to maintain osmoregulation such that pressure within the cells remains relatively constant and this is also vital because it is used to maintain the electrochemical gradient in the cell membrane that provides electrical activity to the membrane. Cells achieve this by maintaining distinct solute concentrations across plasma membranes using active and passive transport as well as diffusion of water molecules.
Taurine is an effective osmoregulatory agent because its structure facilitates this role. Taurine is transported via specific β-amino acid transporters in a sodium ion dependent manner, and very high concentration gradients can be maintained because taurine is highly water soluble and does not cross the plasma membrane outside of its transport system. However, in mammals the role of taurine in osmoregulation is not as great as in other species, for example marine organisms such as fish and invertebrates, which face unique challenges due to the high saline conditions they live in. In contrast taurine in mammals likely plays an accessory role in osmoregulation, with the main role played by inorganic solutes such as sodium ions, potassium ions and chloride ions.
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