L-arginine Transport In Endothelial Cells Research Articles

Thyroid hormones stimulate L-arginine transport in human endothelial cells

Thyroid hormone activity is associated with L-arginine metabolism and nitric oxide (NO) production, which participate in the cardiovascular manifestations of thyroid disorders. L-arginine transporters play an important role in activating L-arginine uptake and NO production. However, the effects of thyroid hormones on L-arginine transporters in endothelial cells have not yet been evaluated. The following methods were used. We measured L-arginine uptake, mRNA expression of L-arginine transporters, endothelial nitric oxide synthase (eNOS) mRNA and NO generation after the administration of T3, T4 and the T3 analog, 3,3′,5-triiodothyroacetic acid TRIAC in human umbilical vein endothelial cells (HUVECs). We also analyzed the role of αvβ3 integrin and of phosphatidyl-inositol-3 kinase (PI3K), mitogen-activated protein kinases (MAPKs: ERK1/2, p38 and SAPK-JNK) and intracellular calcium signaling pathways as underlying mechanisms. To this end, αvβ3 integrin was pharmacologically inhibited by tetraiodothyroacetic acid (TETRAC) or genetically blocked by silencing αv mRNA and PI3K, MAPKs and intracellular calcium by selective inhibitors. The following results were obtained. Thyroid hormones and the T3 analog TRIAC increased L-arginine uptake in HUVECs, the sodium-independent y+/CAT isoforms, except CAT2b, sodium-dependent y+L system and sodium-independent system b0,+L-arginine transporters, eNOS mRNA and NO production. These effects were suppressed by αvβ3 integrin inhibition with TETRAC or αv integrin downregulation or by PI3K, MAPK or intracellular Ca2+ signaling inhibitors. In conclusion, we report for the first time that activation of L-arginine uptake by thyroid hormones is related to an upregulation of L-arginine transporters. This effect seems to be mediated by activation of αvβ3 integrin receptor and subsequent PI3K, MAPK and intracellular Ca2+ signaling pathways.

Panax notoginseng and its components decreased hypertension via stimulation of endothelial-dependent vessel dilatation

Ginsenoside Rb1 and Rg1 are major components of Panax notoginseng (P.N.), an herb with known clinical efficacy in hypertension and myocardial ischemia in Eastern countries. This investigation is to elicit the mechanism of these components in hypertension via their effect on vascular reaction. To assess the ability of P.N. in hypertension, P.N. extracts were injected in spontaneously hypertensive rats (SHR) via the vena caudalis; Low dosages of P.N. extracts significantly lowered blood pressure in SHR. Examination with Rb1 and Rg1 revealed significant vasodilatation using mouse coronary arteries in a dose-dependent manner. Rb1- and Rg1-induced vasodilatation was blocked by pre-incubation with eNOS and PI3K inhibitors. Coronaries of eNOS−/− mice showed attenuated vasodilatation with Rb1 and Rg1. In addition, both Rb1 and Rg1 induce nitric oxide (NO) generation through increasing the phosphorylation of eNOS, activating Na+−independent l-arginine transport, and stimulating cationic amino acid transport (CAT)-1 mRNA expression in cultured endothelial cells. ConclusionGinsenoside Rb1 and Rg1 increased endothelial-dependent vessel dilatation through the activation of NO by modulating the PI3K/Akt/eNOS pathway and l-arginine transport in endothelial cells. These findings may have important implications for understanding the mechanisms of clinical efficacy of the herb P.N. when used in the regulation of blood pressure.

Protein kinase C mediated inhibition of endothelial l-arginine transport is mediated by MARCKS protein

The endothelium plays a vital role in the maintenance of vascular tone and structural vascular integrity, principally mediated via the actions of nitric oxide (NO). l-arginine is the immediate substrate for NO synthesis, and the availability of extracellular l-arginine is critical for the production of NO. Activation of protein kinase C (PKC) dependent signalling pathways are a feature of a number of cardiovascular disease states, and in this study we aimed to systematically evaluate the mechanism by which PKC regulates l-arginine transport in endothelial cells. In response to PKC activation (PMA 100 nM, 30 min), [ 3H] l-arginine uptake by bovine aortic endothelial cells (BAEC) was reduced to 45 + 4% of control ( p < 0.05). This resulted from a 53% reduction in the Vmax ( p < 0.05), with no change in the K m for l-arginine. Western blot analysis and confocal microscopy revealed no change in the expression or membrane distribution of CAT-1, the principal BAEC l-arginine transporter. Moreover in 32P-labeling studies, PMA exposure did not result in CAT-1 phosphorylation. We therefore explored the possibility that PKC altered and interaction with MARCKS protein, a candidate membrane associated protein. By co-immunoprecipitation we show that CAT-1 interacts with, a membrane associated protein, that was significantly inhibited by PKC activation ( p < 0.05). Moreover antisense inhibition of MARCKS abolished the PMA effect on l-arginine transport. PKC dependent mechanisms regulate the transport of l-arginine, mediated via process involving MARCKS.

L-Arginine transport in endothelial cells

L-Arginine transport in endothelial cells