Peptide uptake by astroglia-rich brain cultures

Uptake of carnosine has been investigated in astroglia-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 Km = 50 microM and Vmax = 22.7 nmol X h-1 X mg protein-1. Uptake of carnosine is strongly inhibited by other dipeptides as well as by various oligopeptides, e.g., Leu-enkephalin. However, uptake of the radiolabeled tripeptide D-Ala-L-Ala-L-Ala was not observed. Radiolabeled Leu-enkephalin 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.