Activation of L-arginine transport (system y(+)) and nitric oxide synthase by elevated glucose and insulin in human endothelial cells

1. Modulation of L-arginine transport (system y(+)) and release of nitric oxide (NO) and prostacyclin (PGI(2)) by elevated glucose and insulin were investigated in human cultured umbilical vein endothelial cells. 2. Elevated glucose induced a time- (6-12 h) and concentration-dependent stimulation of L-arginine transport, which was reversible and associated with a 3-fold increase in intracellular cGMP accumulation (index of NO synthesis) and 75% decrease in PGI(2) production. 3. Elevated glucose had no effect on the initial transport rates for L-serine, L-citrulline, L-leucine, L-cystine or 2-deoxyglucose. 4. Resting membrane potential was unaffected by elevated glucose whereas basal intracellular [Ca2+] increased from 65 +/- 5 nM to 136 +/- 16 nM. 5. Insulin induced a protein synthesis-dependent stimulation of L-arginine transport and increased NO and PGI(2) production in cells exposed to 5 mM glucose. 6. In cells exposed to high glucose, insulin downregulated elevated rates of L-arginine transport and cGMP accumulation but had no effect on the depressed PGI(2) production. 7. Our findings suggest that insulin's normal stimulatory action on human endothelial cell vasodilator pathways may be impaired under conditions of sustained hyperglycaemia.