Amino acid uptake by bovine mammary slices

A method which measures amino acid uptake by bovine mammary slices is described. Slices of approximately 200 mg were preincubated for 1 h in a modified Krebs-Ringers bicarbonate buffer containing a physiological mixture of amino acids. After preincubation, slices were incubated with radioactive amino acid for 10 min. Slices then were homogenized in perchloric acid, centrifuged, and a sample of the supernate was counted for radioactivity. In parallel experiments, the percent tissue water was determined by drying slices to constant weight. Extra-cellular space of slices was measured with inulin. These measurements allowed uptake to be expressed in terms of amino acid concentration in the cell water. The in vitro uptake pattern of nine essential amino acids was compared to the known in vivo uptake pattern of these amino acids by the cow udder. The correlation between in vitro and in vivo uptake patterns was .91, suggesting that the tissue slice technique can be useful in further study of bovine mammary amino acid transport.