Peptide Uptake by Astroglia-Rich Brain Cultures

Abstract: Uptake of carnosine has been investigated in as-troglia-rich primary cultures derived from brains of newborn mice. It could be demonstrated that carnosine is not degraded by these cells but rapidly taken up in an energy and sodium-dependent process. Uptake and release of carnosine by these cells were found to be mediated by a saturable, high-affinity transport system with apparent kinetic constants of K_m=50 μMand V_max= 22.7 nmol h¹ mg protein¹. Uptake of carnosine is strongly inhibited by other dipeptides as well as by various oligopeptides, e.g., Leu-en-kephalin. However, uptake of the radiolabeled tripeptide D Ala-L-Ala-L-Ala was not observed. Radiolabeled Leu-en-kephalin also did not accumulate intracellularly, even if degradation of the peptide was prevented by use of peptidase inhibitors. These results suggest that uptake of carnosine is catalyzed by a dipeptide-specific transport system with broad substrate specificity. With neuronal cells in primary culture, uptake of carnosine or other peptides was not observed.