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and System A Amino Acid Transporters in the Feline Endotheliochorial Placenta
1 Academic Unit of Child Health, University of Manchester, Manchester, United Kingdom
2 Waltham Centre for Pet Nutrition, Waltham on the Wolds, Melton Mowbray, Leicestershire, United Kingdom
3 Academic Unit of Obstetrics and Gynaecology, University of Manchester, Manchester, United Kingdom
* To whom correspondence should be addressed. E-mail: susan.greenwood{at}man.ac.uk.
There is no knowledge of the transport mechanisms by which solutes cross the cat placenta, or any other endotheliochorial placenta. Here we investigated whether the amino acid transport systems 
and A are present in the cat placenta using a placental fragment uptake technique. Data were compared to studies in the human placenta, in which the presence of these two transport systems has been well established. A time course of [3H]taurine (substrate for system ) and [14C]MeAIB (non-metabolisable substrate for system A) uptake was determined in the term cat and human placental fragments in the presence and absence (choline substituted) of Na+ and further studies were carried out over 15 minutes. Taurine uptake into both cat and human placenta fragments was found to be Na+- and Cl--dependent and Na+-dependent taurine uptake was blocked by excess -alanine. MeAIB uptake was found to be Na+-dependent and Na+-dependent MeAIB uptake was blocked by excess MeAIB or glycine. Western blotting and immunohistochemistry performed on cat and human placenta showed expression of TAUT and ATA2, proteins associated with system and system A activity respectively. This study therefore provides the first evidence of the presence of amino acid transport systems and A in the cat placenta.
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