Modulation of the cationic amino acid transport system y+L by surface potential, ouabain and thrombin in human platelets: effects of uremia.
BACKGROUND
Nitric oxide (NO), a key endogenous mediator involved in the maintenance of platelet function, is synthesized from the amino acid L-arginine. We have shown that L-arginine transport in platelets is rate-limiting for NO synthesis. A disturbance in the L-arginine-NO pathway in platelets was previously described in chronic renal failure (CRF) patients.


METHODS
Detailed kinetic studies were performed in platelets from controls (n = 60) and hemodialysis patients (n = 26).


RESULTS
The transport of L-arginine in platelets is mediated via system y+L, which is competitively inhibited by L-leucine in the presence of Na+ and by the irreversible inhibitor pCMB. In platelets, system y+L is markedly stimulated by an Na+/K+-ATPase inhibitor, ouabain, and by changes in surface potential, while it is downregulated by intraplatelet amino acid depletion (zero-trans) and by thrombin. In CRF patients, activation of L-arginine transport was limited to well-nourished patients compared to malnourished patients and controls, where it was reduced and did not differ significantly among the groups under zero-trans conditions.


CONCLUSIONS
Our results provide the first evidence that system y+L in platelets is modulated by zero-trans conditions, surface potential, thrombin and intraplatelet Na+ concentration. Our findings suggest that enhanced transport in CRF involves increased L-arginine exchange with intraplatelet neutral amino acids.
Alves de Sá Siqueira
Mariana
M
Departamento de Farmacologia e Psicobiologia, Universidade do Estado do Rio de Janeiro, Rio de Janeiro, Brazil.
Martins
Marcela Anjos
MA
Rodrigues Pereira
Natália
N
Bandeira Moss
Monique
M
Santos
Sérgio F F
SF
Mann
Giovanni E
GE
Mendes-Ribeiro
Antônio C
AC
Brunini
Tatiana M C
TM
D000328:Adult; D027241:Amino Acid Transport System y+L / Q000378:metabolism*; D001120:Arginine / Q000493:pharmacokinetics; D001692:Biological Transport / Q000187:drug effects / Q000502:physiology; D001792:Blood Platelets / Q000187:drug effects* / Q000378:metabolism; D004791:Enzyme Inhibitors / Q000494:pharmacology*; D005947:Glucose / Q000494:pharmacology; D006490:Hemostatics / Q000494:pharmacology*; D006801:Humans; D066298:In Vitro Techniques; D007676:Kidney Failure, Chronic / Q000378:metabolism; D008070:Lipopolysaccharides / Q000494:pharmacology; D008564:Membrane Potentials; D009569:Nitric Oxide / Q000378:metabolism; D010042:Ouabain / Q000494:pharmacology*; D012964:Sodium / Q000378:metabolism; D013917:Thrombin / Q000494:pharmacology*; D014316:Tritium; D014409:Tumor Necrosis Factor-alpha / Q000494:pharmacology; D014511:Uremia / Q000378:metabolism*
D027241:Amino Acid Transport System y+L; D004791:Enzyme Inhibitors; D006490:Hemostatics; D008070:Lipopolysaccharides; D014409:Tumor Necrosis Factor-alpha; D014316:Tritium; D009569:Nitric Oxide; D010042:Ouabain; D001120:Arginine; D012964:Sodium; D013917:Thrombin; D005947:Glucose