Role of osmoregulation in the actions of taurine

Taurine regulates an unusual number of biological phenomena, including hear t rhythm, contractile function, blood pressure, platelet aggregation, neuro nal excitability, body temperature, learning, motor behavior, food consumpt ion, eye sight, sperm motility, cell proliferation and viability, energy me tabolism and bile acid synthesis. Many of these actions are associated with alterations in either ion transport or protein phosphorylation. Although t he effects on ion transport have been attributed to changes in membrane str ucture, they could be equally affected by a change in the activity of the a ffected transporters. Three common ways of altering transporter activity is enhanced expression, changes in the phosphorylation status of the protein and cytoskeletal changes. Interestingly, all three events are altered by os motic stress. Since taurine is a key organic osmolyte in most cells, the po ssibility that the effects of taurine on ion transport could be related to its osmoregulatory activity was considered. This was accomplished by compar ing the effects of taurine, cell swelling and cell shrinkage on the activit ies of key ion channels and ion transporters. The review also compares the phosphorylation cascades initiated by osmotic stress with some of the phosp horylation events triggered by taurine depletion or treatment. The data rev eal that certain actions of taurine are probably caused by the activation o f osmotic-linked signaling pathways. Nonetheless, some of the actions of ta urine are unique and appear to be correlated with its membrane modulating a nd phosphorylation regulating activities.