Platelet taurine concentration and uptake in the Brattleboro diabetes insipidus rat

Since platelets accumulate taurine, they provide a model for studying the taurine transport in anisosmotic disorders. Thus, in this work we studied the taurine concentration and uptake in the platelets of Brattleboro rats, homozygous (DI) and heterozygous (HZ) for hereditary hypothalamic diabetes insipidus, and Long Evans (LE) normal rats after free water intake and after dehydration induced by water deprivation for 24 h. The decreased ability of the DI rats to concentrate urine led to plasma hypernatremia and hyperosmolality despite excessive drinking. Water deprivation in the DI rats induced drastic dehydration with exacerbated hypernatremia and hyperosmolality. Plasma hypernatremia and hyperosmolality resulted in a significant elevation of the taurine concentration and uptake by platelets of the DI rats. Kinetic assays showed that plasma hypernatremia and hyperosmolality did not alter the affinity of taurine to platelet membrane carrier, as expressed by Km, but caused a profound increase in the maximal transport capacity, Vmax. After free water intake the Vmax of the DI rats was about two times higher than that in the HZ and LE rats and after water deprivation it was about three times higher. Water deprivation doubled the Vmax of the DI rats without changing the Km.