Transport of L-arginine and nitric oxide formation in human platelets

The results of the present study show that human platelets take up l-arginine by two transport systems which are compatible with the systems y(+) and y(+) L. These Na+ independent transporters have been distinguished by treating platelets with N -ethylmaleimide that blocks selectively system y(+) . System y(+) , that accounts for 30-40% of the total transport, is characterized by low affinity for l-arginine, is unaffected by l-leucine, is sensitive to changes of membrane potential and to trans -stimulation. The other component of l-arginine transport identified with the system y(+) L (approximately 60-70% of the total flux) shows high affinity for l-arginine, is insensitive to N -ethylmaleimide treatment, unaffected by changes in membrane potential, sensitive to trans -stimulation and inhibited by l-leucine in the presence of Na+ . Moreover a strict correlation between l-arginine transport and nitric oxide (NO) production in whole cells was found. N -ethylmaleimide and l-leucine decreased NO production as well as cGMP elevation, and the effect on NO and cGMP were closely related. It is likely that the l-arginine transport systems y(+) and y(+) L are both involved in supplying substrate for NO production and regulation in human platelets.