Peptide Uptake by Astroglia‐Rich Brain Cultures

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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 Km=50 μMand Vmax= 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.