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pubmed:abstractText |
1. The role of protein kinase C in controlling L-arginine transport in alveolar macrophages was investigated. 2. L-[3H]Arginine uptake in rabbit alveolar macrophages declined by 80 % after 20 h in culture. 4beta-Phorbol 12-myristate 13-acetate (PMA), but not 4alpha-phorbol 12-myristate 13-acetate (alpha-PMA), present during 20 h culture, enhanced L-[3H]arginine uptake more than 10-fold. Staurosporine and chelerythrine opposed this effect. 3. L-[3H]Arginine uptake was saturable and blockable by L-lysine. After PMA treatment Vmax was increased more than 5-fold and Km was reduced from 0.65 to 0.32 mM. 4. Time course experiments showed that PMA increased L-[3H]arginine uptake almost maximally within 2 h. This short-term effect was not affected by cycloheximide or actinomycin D. 5. L-[3H]Arginine uptake and its stimulation by PMA was also observed in sodium-free medium. 6. L-Leucine (0.1 mM) inhibited L-[3H]arginine uptake by 50 % in sodium-containing medium, but not in sodium-free medium. At 1 mM, L-leucine caused significant inhibition in sodium-free medium also. L-Leucine showed similar effects on PMA-treated cells. 7. N-Ethylmaleimide (200 microM, 10 min) reduced L-[3H]arginine uptake by 70 % in control cells, but had no effect on PMA-treated (20 or 2 h) cells. 8. In alveolar macrophages, multiple transport systems are involved in L-arginine uptake, which is markedly stimulated by protein kinase C, probably by modulation of the activity of already expressed cationic amino acid transporters.
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