S-nitrosoglutathione/glutathione disulphide/Cu2+-dependent stimulation of L-arginine transport in human platelets

In this study, we have examined the effects of authentic nitric oxide (NO), NO+ (NOBF4), glutathione (GSH), glutathione disulphide (GSSG), and S-nitrosoglutathione (GSNO) in the presence and absence of Cu2+, which thermally releases NO from S-nitrosothiols on the transport of L-arginine into the human platelet. The K-M,K-apparent was unaffected by NO, NO+, GSH, and GSNO. However, Cu2+ lowered K-M,K-apparent by similar to 2.85-fold. Cu2+-dependent lowering of KIM: apparent was also observed, albeit to a smaller extent when this ion was mixed with GSH (similar to 1.9-fold lower) and GSNO (similar to 2.0-fold). GSSG also lowered K-M,K-apparent by similar to 1.5-fold. The V-max,V-apparent of L-arginine uptake was unaffected by NO, NO+, GSH, and Cu2+. Vmax,apparent was stimulated by to the largest extent by GSNO (similar to 2.28-fold) and GSNO plus Cu2+ (similar to 2.7-fold). GSSG and GSH plus Cu2+ also increased V-max,V-apparent by similar to 1.9-fold. When these parameters are expressed in terms of transport efficiency (V-max/K-M) the largest effect of nearly 4.7-fold (over controls) was obtained by a combination of GSNO plus Cu2+. These results suggest that platelet L-Arg transport is not affected either by NO or NO+ but by a thiol-disulphide exchange reactions on the platelet L-Arg transporter, brought about by GSNO and GSSG. Based on these results, a GSNO/GSSG/Cu2+ dependent regulatory mechanism for the uptake of L-arginine in human platelets has been proposed. (C) 1998 Elsevier Science Ltd.