Modulation of the L-arginine/nitric oxide signalling pathway in vascular endothelial cells

摘要

Nitric oxide (NO) is synthesized from L-arginine,and in endothelial cells influx of L-arginine is mediated predominantly via Na~+-independent cationic amino acid transporters.Constitutive,Ca~(2+)-calmodulin-sensitive eNOS (endothelial nitric oxide synthase) metabolizes L-arginine to NO and L-citrulline.eNOS is present in membrane caveolae and the cytosol and requires tetrahydrobiopterin,NADPH,FAD and FMN as additional cofactors for its activity.Supply of L-arginine for NO synthesis appears to be derived from a membrane-associated compartment distinct from the bulk intracellular amino acid pool,e.g.near invaginations of the plasma membrane referred to as 'lipid rafts' or caveolae.Co-localization of eNOS and the cationic amino acid transport system y~+ in caveolae in part explains the 'arginine paradox',related to the phenomenon that in certain disease states eNOS requires an extracellular supply of L-arginine despite having sufficient intracellular L-arginine concentrations.Vasoactive agonists normally elevate [Ca~(2+)];(intracellular calcium concentration) in endothelial cells,thus stimulating NO production,whereas fluid shear stress,17beta-oestradiol and insulin cause phosphorylation of the serine/threonine protein kinase Akt/protein kinase B in a phosphoinositide 3-kinase-dependent manner and activation of eNOS at basal [Ca~(2+)];levels.Adenosine causes an acute activation of p42/p44 mitogen-activated protein kinase and NO release,with membrane hyperpolarization leading to increased system y~+ activity in fetal endothelial cells.In addition to acute stimulatory actions of D-glucose and insulin on L-arginine transport and NO synthesis,gestational diabetes,intrauterine growth retardation and pre-eclampsia induce phenotypic changes in the fetal vasculature,resulting in alterations in the L-arginine/NO signalling pathway and regulation of [Ca~(2+)]_i.These alterations may have significant implications for long-term programming of the fetal cardiovascular system.