Characterization of L-DOPA transport in cultured rat and mouse astrocytes.
The present work studied the transport of L-DOPA in cultured rat and mouse astrocytes. Results indicated that the uptake of L-[14C]DOPA in both rat and mouse astrocytes was Na+ independent and temperature sensitive. It was mediated by a carrier-mediated mechanism with Km values of 36 and 60.3 microM, and V(max) values of 2.4 and 1.9 nmol/min/mg protein for rat and mouse cells, respectively. L-DOPA uptake was potently inhibited by aromatic or branched-chain amino acids. Interestingly, the release of intracellular L-[14C]DOPA was also trans stimulated by competitors that affect L-DOPA uptake. The 14C recovered in the 2-min uptake process was identified as L-[14C]DOPA. However, [14C]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 decarboxylase (AADC). Taken together, L-DOPA was uphill transported into rat and mouse astrocytes by a (Na+) -independent exchanger with preference for aromatic and branched-chain amino acids. Rat astrocytes possessed higher affinity for L-DOPA uptake than mouse astrocytes. 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 machinery. These results may be of particular importance to parkinsonian patients under L-DOPA medication.
Tsai
M J
MJ
Institute of Biomedical Sciences, Academia Sinica, Taipei, Taiwan, Republic of China.
Lee
E H
EH
D000596:Amino Acids / Q000494:pharmacology; D000818:Animals; D001142:Aromatic-L-Amino-Acid Decarboxylases / Q000032:analysis; D001253:Astrocytes / Q000378:metabolism*; D001692:Biological Transport / Q000502:physiology; D002478:Cells, Cultured; D007700:Kinetics; D007980:Levodopa / Q000378:metabolism / Q000493:pharmacokinetics*; D051379:Mice; D008810:Mice, Inbred C57BL; D051381:Rats; D017207:Rats, Sprague-Dawley; D012964:Sodium / Q000494:pharmacology; D013045:Species Specificity; D013696:Temperature
D000596:Amino Acids; D007980:Levodopa; D012964:Sodium; D001142:Aromatic-L-Amino-Acid Decarboxylases