Characterization of transport systems for the transfer of 3,4-L-dihydroxyphenylalanine into slices of rat cerebral cortex.
1. Slices of rat cerebral cortex incubated aerobically at 37 degrees C in Krebs-Ringer-bicarbonate solution accumulated 3,4-L-dihydroxyphenylalanine (L-DOPA) against its concentration gradient. With 1 mM L-DOPA in the medium, tissue-water/medium concentration ratios of about 6 : 1 are reached, which are modified by the presence of other amino acids in the medium. 2. Kinetic analysis suggested that L-DOPA influx into brain cells occurred by at least two saturable processes, which show apparent Km values in the range of 10(-3) M and 10(-5) M, respectively. 3. Prior incubation of the slices in Na+-free (choline-containing) medium at 37 degrees C depressed their subsequent uptake of L-DOPA in normal Na+-containing medium; this inhibition did not appear when the preincubation was carried out at 0-4 degrees C. Besides this effect of preincubation, most of L-DOPA influx into brain slices was independent of the actual concentration of Na+ in the medium; the two saturable processes described in this article behaved similarly in this respect. 4. Most of L-DOPA uptake by the high-Km process is mediated by an agency that resembles the Na+-independent L system described in Ehrlich cells (Oxender, D. L. and Christensen, H. N. (1963) J. Biol. Chem. 238, 2686-2699), both in its specificity and in its participation in exchange phenomena. A lesser component of uptake by a type A mediation is also suggested as contributing to the high-Km process . 5. The kinetic and specificity properties of the low-Km process of L-DOPA uptake suggest a similarity between its mediation and that of the high-affinity systems for L-tyrosine and L-tryptophan found in brain tissue preparations (Belin, M. F. and Pujol, J. F. (1973) Experientia 29, 411-413; Bauman, A., Bourgoin, S., Benda, P., Glowinski, J. and Hamon, M. (1971 Brain Res. 66, 253-263).
D000409:Alanine / Q000494:pharmacology; D000596:Amino Acids / Q000494:pharmacology; D000818:Animals; D001692:Biological Transport / Q000187:drug effects; D002540:Cerebral Cortex / Q000378:metabolism*; D006639:Histidine / Q000494:pharmacology; D007700:Kinetics; D007930:Leucine / Q000494:pharmacology; D007980:Levodopa / Q000378:metabolism*; D008297:Male; D011188:Potassium / Q000494:pharmacology; D051381:Rats; D012964:Sodium / Q000494:pharmacology
D000596:Amino Acids; D007980:Levodopa; D006639:Histidine; D012964:Sodium; D007930:Leucine; D000409:Alanine; D011188:Potassium