Changes in kinetics of amino acid uptake at the ageing ovine blood–cerebrospinal fluid barrier

Kinetics study of AA uptake into young and old CP. Phe and Lys uptakes into old CP had significant higher kinetics (both K_m and V_max) than the young, and while Leu and Ala uptakes into old CP were similar to the young. Solid symbols were from young preparation while open symbols were from the old.

Cross-competition of AA uptake into young and old CP. In young sheep, Leu uptake was significantly inhibited by Phe and vice versa. Ala uptake can be inhibited by 5mM Leu. In old sheep, Leu and Phe interacted each other significantly but only at highest concentration (i.e. 5mM). *Means p<0.05, **indicates p<0.01 in comparison of the control value. Solid symbols were from young preparation while open symbols were from the old. The presence of Leu, Phe, Ala, Lys were represented, respectively, by symbols (■, ♦, ●, ▴.).

An example of the recovery of ¹⁴C-mannitol vs. ³H-mannitol (A), or ¹⁴C-Lys vs. ³H-Lys (B), or ¹⁴C-mannitol vs. ³H-Lys (C), or ¹⁴C-Lys vs. ³H-mannitol (D), in one run of 20 venous samples plotted as a percentage of total radioactivity injected and against time. There were almost identical curves in A and B. The lower recovery of Lys relative to mannitol in C and D indicates cellular uptake of Lys at the basolateral face of the CP. The net uptake of Lys was not different between C and D.