CHARACTERIZATION OF L-DOPA TRANSPORT IN CULTURED RAT AND MOUSE ASTROCYTES

The present work studied the transport of L-DOPA in cultured rat and m ouse astrocytes. Results indicated that the uptake of L-[C-14]DOPA in both rat and mouse astrocytes was Na+ independent and temperature sens itive, It was mediated by a carrier-mediated mechanism with K-m values of 36 and 60.3 mu M, and V-max values of 2.4 and 1.9 nmol/min/mg prot ein for rat and mouse cells, respectively. L-DOPA uptake was potently inhibited by aromatic or branched-chain amino acids, Interestingly, th e release of intracellular L-[C-14]DOPA was also trans stimulated by c ompetitors that affect L-DOPA uptake, The C-14 recovered in the 2-min uptake process was identified as L-[C-14]DOPA, However, [C-14]dopamine (DA) was also detected in both rat and mouse astrocytes after 30 min L-DOPA incubation, indicating the existence of aromatic L-amino acid d ecarboxylase (AADC), Taken together, L-DOPA was uphill transported int o rat and mouse astrocytes by a Naf-independent exchanger with prefere nce for aromatic and branched-chain amino acids, Rat astrocytes posses sed higher affinity for L-DOPA uptake than mouse astrocyte, Both cells synthesized DA from exogenous L-DOPA, Thus, astrocytes serve not only as a temporary storage site for L-DOPA but also as a DA-producing mac hinery, These results may be of particular importance to parkinsonian patients under L-DOPA medication. (C) 1996 Wiley-Liss, Inc.