Regulatory pathways and uptake of L-DOPA by capillary cerebral endothelial cells, astrocytes, and neuronal cells.
We examined the nature and regulation of the inward L-3,4-dihydroxyphenylalanine (L-DOPA) transporter in rat capillary cerebral endothelial (RBE4) cells, type 1 astrocytes (DI TNC1), and Neuro-2a neuroblastoma cells. In all three cell types, the inward transfer of L-DOPA was largely promoted through the 2-aminobicyclo-(2,2,1)-heptane-2-carboxylic acid-sensitive and sodium-independent L-type amino acid transporter. Only in DI TNC1 cells was the effect of maneuvers that increase intracellular cAMP levels accompanied by increases in L-DOPA uptake. Also, only in DI TNC1 cells was the effect of the guanylyl cyclase inhibitor LY-83583 accompanied by a 65% increase in L-DOPA accumulation, whereas the nitric oxide donor sodium nitroprusside produced a 25% decrease in L-DOPA accumulation. In all three cell types, the Ca2+/calmodulin inhibitors calmidazolium and trifluoperazine inhibited L-DOPA uptake in a noncompetitive manner. Thapsigargin (1 and 3 microM) and A-23187 (1 and 3 microM) failed to alter L-DOPA accumulation in RBE4 and Neuro-2a cells but markedly increased L-DOPA uptake in DI TNC1 cells. We concluded that L-DOPA in RBE4, DI TNC1, and Neuro-2a cells is transported through the L-type amino acid transporter and appears to be under the control of Ca2+/calmodulin-mediated pathways. Astrocytes, however, are endowed with other processes that appear to regulate the accumulation of L-DOPA, responding positively to increases in intracellular Ca2+ and cAMP and to decreases in cGMP.
Sampaio-Maia
B
B
Institute of Pharmacology and Therapeutics, Faculty of Medicine, 4200-319 Porto, Portugal.
Serrão
M P
MP
Soares-da-Silva
P
P
D000818:Animals; D015703:Antigens, CD / Q000378:metabolism; D001253:Astrocytes / Q000166:cytology / Q000378:metabolism*; D001921:Brain / Q000378:metabolism*; D002118:Calcium / Q000378:metabolism; D002352:Carrier Proteins / Q000378:metabolism; D002460:Cell Line; D000242:Cyclic AMP / Q000378:metabolism; D006152:Cyclic GMP / Q000378:metabolism; D015259:Dopamine Agents / Q000493:pharmacokinetics*; D004730:Endothelium, Vascular / Q000166:cytology / Q000378:metabolism*; D027261:Fusion Regulatory Protein-1; D007980:Levodopa / Q000493:pharmacokinetics*; D009474:Neurons / Q000166:cytology / Q000378:metabolism*; D051381:Rats
D015703:Antigens, CD; D002352:Carrier Proteins; D015259:Dopamine Agents; D027261:Fusion Regulatory Protein-1; D007980:Levodopa; D000242:Cyclic AMP; D006152:Cyclic GMP; D002118:Calcium