Nitric oxide synthesis requires activity of the cationic and neutral amino acid transport system y(+)L in human umbilical vein endothelium

L-Arginine transport is mediated by the cationic/neutral amino acid transport system y(+)L and cationic amino acid transporters y(+)/CATS in human umbilical vein endothelial cells (HUVECs). System y(+)/CATS activity may be rate-limiting for nitric oxide (NO) synthesis, but no reports have demonstrated system y(+)L involvement in NO synthesis in endothelium. We investigated the role of system y(+)L in NO synthesis in HUVECs. Transport of 1.5 muM L-arginine was inhibited (P 0.05) by L-alanine or L-cysteine. The system y(+)/CATS inhibitor, N-ethylmaleimide (NEM), did not alter 1.5 muM L-arginine transport, but inhibited (92 +/- 3 %) 100 muM L-arginine transport. L-Arginine transport in the presence of NEM was saturable (V-max, 0.37 +/- 0.02 pmol (mug protein)(-1) min(-1); K-m, 1.5 +/- 0.3 muM) and competitively inhibited by L-leucine in the presence of Na+ (V-max, 0.49 +/- 0.06 pmol (mug protein)(-1) min(-1); K-m, 6.5 +/- 0.9 muM). HUVECs express SLC3A2/4F2hc, SLC7A7/4F2-lc2 and SLC7A6/4F2-lc3 genes encoding for the high-affinity transport system y(+)L. N-G-Nitro-L-arginine methyl ester and L-leucine, but not NEM, inhibited NO synthesis in medium containing 1.5 muM L-arginine. Cells exposed to 25 MM D-glucose (24 h) exhibited reduced system y(+)L activity (V-max, 0.15 +/- 0.008 pmol (mug protein)(-1) min(-1); K-m, 1.4 +/- 0.3 muM) and NO synthesis. However, 25 HIM D-glucose increased NO synthesis and L-arginine transport via system y(+). Thus, L-arginine transport through system y(+)L plays a role in NO synthesis, which could be a determining factor in pathological conditions where the endothelial L-arginine-NO pathway is altered, such as in diabetes mellitus

Heteromeric Solute Carriers: Function, Structure, Pathology and Pharmacology

Solute carriers form one of three major superfamilies of membrane transporters in humans, and include uniporters, exchangers and symporters. Following several decades of molecular characterisation, multiple solute carriers that form obligatory heteromers with unrelated subunits are emerging as a distinctive principle of membrane transporter assembly. Here we comprehensively review experimentally established heteromeric solute carriers: SLC3-SLC7 amino acid exchangers, SLC16 monocarboxylate/H+ symporters and basigin/embigin, SLC4A1 (AE1) and glycophorin A exchanger, SLC51 heteromer Ost α-Ost β uniporter, and SLC6 heteromeric symporters. The review covers the history of the heteromer discovery, transporter physiology, structure, disease associations and pharmacology - all with a focus on the heteromeric assembly. The cellular locations, requirements for complex formation, and the functional role of dimerization are extensively detailed, including analysis of the first complete heteromer structures, the SLC7-SLC3 family transporters LAT1-4F2hc, b0,+AT-rBAT and the SLC6 family heteromer B0AT1-ACE2. We present a systematic analysis of the structural and functional aspects of heteromeric solute carriers and conclude with common principles of their functional roles and structural architecture