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

Published online by Cambridge University Press:  01 June 2009

David B. Shennan
Affiliation:
Hannah Research Institute, Ayr KA6 5HL, UK
Sandra A. McNeillie
Affiliation:
Hannah Research Institute, Ayr KA6 5HL, UK

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. The Ka and Vmax of 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.

Type
Original Articles
Copyright
Copyright © Proprietors of Journal of Dairy Research 1994

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