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RESEARCH PRODUCT

[9] Identification of carrier systems in plasma membranes of mammalian cells involved in transport of l-arginine

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Publisher Summary This chapter describes the transport systems and the corresponding carrier proteins involved in the L-arginine transport that have been described till date. The chapter also discusses the methods that have been used to characterize L-arginine transport in nitric oxide (NO) producing cells or tissues. L-arginine transport is mediated by multiple carrier systems, some of which have not yet been identified at a molecular level. It is conceivable that a modification of a carrier or an associated protein could alter its transport activity, resulting in the appearance of a carrier with altered transport characteristics. Considerable progress has been made in identifying cationic L-amino acids (CAA) carrier systems and proteins and their expressional regulation in NO-producing cells. However, to understand the role of each of these proteins in supplying substrate for NO synthesis, specific inhibitors or antisense probes are required to inhibit the expression of these proteins. The precise localization of CAA carriers in distinct membrane areas remains unresolved and the hypothetical compartmentalization of L-arginine within cells may explain the dependence of NO synthesis in certain cells on extracellular L-arginine despite saturating intracellular L-arginine levels. The immunocytochemical localization of constitutive endothelial NOS (eNOS) in plasmalemmal caveolae suggests that NO signaling may be restricted to specific targets within a limited microenvironment at the cell surface and, if L-arginine transporter(s) were also expressed in caveolae, this would significantly restrict availability of extracellular L-arginine.