High affinity (Na++ Cl-)-dependent taurine transport by lactating mammary tissue

Publisher Website
Google Scholar
Abstract
Summary: The transport of taurine by lactating rat mammary tissue has been examined. Taurine uptake was found to be dependent upon the presence of extracellular Na+and Cl-, which is consistent with (Na++ Cl-+ taurine) cotransport. TheKaandVmaxof taurine influx were respectively 43 μM and 37·5 μmol/kg cell water per 15 min. It is apparent that the mechanism responsible for taurine uptake is highly selective for β-amino acids. Taurine efflux consisted of a fast extracellular component and a slow membrane-limited component. The slow component was relatively insensitive to temperature, suggesting that it may represent simple diffusion. Mammary tissue was found to contain a high level of intracellular taurine: 7·29–7·44 mmol/kg cell water. We suggest that taurine is taken up and concentrated by the mammary gland by a (Na++ Cl-+ taurine) cotransport mechanism situated in the blood-facing aspect of the secretory epithelium and that a low outward permeability to taurine allows a high intra-to-extracellular concentration gradient to be maintained. Milk taurine may be derived from taurine diffusing from the cell cytosol across the apical membrane.