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K Posch

Publications and source records attributed to K Posch.

7 recordsLinked to original sources
PubMed1999

Selective stimulation of L-arginine uptake contributes to shear stress-induced formation of nitric oxide.

The aim of this study was to investigate the kinetics of L-arginine transport mechanisms and the role of extracellular L-arginine in nitric oxide formation during shear stress activation of endothelial cells. Porcine aortic endothelial cells were grown to confluence and were exposed to various amounts of shear stress for 40 min. Formation of nitric oxide was monitored by measuring elevation of endothelial cGMP. Activity of amino acid transport systems was determined by measuring the uptake of L-[3H]leucine (L system) and L-[3H]arginine (y+) under resting and shear stress condition. Shear stress-mediated nitric oxide formation critically depended on the presence of extracellular L-arginine, which increased shear stress-induced cGMP increases in a concentration dependent manner (EC50=123 microM). In addition, shear stress increased L-arginine uptake, while the transport capacity for neutral amino acids (L system) remained unchanged under shear stress conditions. Analysis of the kinetics of the uptake of L-arginine under resting and shear stress conditions indicate that shear stress increased velocity of the high affinity, low capacity transport (y+) without affecting affinity of this system. These data suggest that shear stress selectively activates uptake of L-arginine in endothelial cells and that the uptake of L-arginine might be important for shear stress-mediated nitric oxide formation.

Adenosine Diphosphate↗
PubMed1999

Increased superoxide anion formation in endothelial cells during hyperglycemia: an adaptive response or initial step of vascular dysfunction?

In diabetes mellitus, the risk for cardiovascular complications and development of atherosclerosis is increased compared with healthy individuals. Recently evidence was provided that increased production of superoxide anions occurs in endothelial cells during hyperglycemia. In order to evaluate the potential impact of the enhanced formation of this oxygen radical for vascular cell dysfunction and its role in tissue adaptation, it is essential to assess the effect of superoxide anions on endothelial cell function. Here, we present new data and review our previous work on the effects of superoxide anions on endothelial vascular function, such as intracellular Ca2+ signal cascade, formation and bioactivity of nitric oxide. Based on the presented data we discuss superoxide anion production as a two faced phenomenon. In lower concentrations, superoxide anions are mediators of an endothelium adaptation to ensure endothelial vasomotion control. However, in higher concentrations superoxide anions disrupt endothelial-smooth muscle crosstalk resulting in vessel wall dysfunction and vascular wall dysfunction.

Adaptation, Physiological↗
PubMed1999

Glycated low-density lipoprotein attenuates shear stress-induced nitric oxide synthesis by inhibition of shear stress-activated L-arginine uptake in endothelial cells.

Little is known about the mechanism(s) of endothelial dysfunction in diabetes. In this study, the effect of nonenzymatic glycated LDL, a phenomenon induced by elevated D-glucose levels associated with diabetes, on porcine aortic endothelial cells was investigated. Two fractions of LDL from diabetic patients were separated by affinity column chromatography and are referred to herein as fraction alpha (nonglycated LDL) and fraction beta (glycated LDL). Incubation of endothelial cells for 24 h with total LDL isolated from diabetic subjects (dLDL) increased the release of superoxide anions (*O2-) by fivefold, while no effect of LDL isolated from healthy individuals (nLDL) was found. Fraction beta, but not fraction alpha, evoked the *O2- release. In vitro-glycated LDL mimicked the effect of dLDL/fraction beta on *O2- release that correlated with its degree of glycation (R2 = 0.96). Moreover, nitric oxide (NO) stability (measured with a porphyrinic-based electrode) and NO bioactivity (measured by its ability to elevate cellular cGMP levels) were reduced in cells treated with dLDL by 46 and 41%, respectively. dLDL (but not nLDL or fraction alpha) abolished shear stress-induced L-arginine uptake. The inhibitory effect of dLDL on shear stress-induced L-arginine uptake was mimicked by in vitro-glycated LDL. The efficiency of in vitro-glycated LDL to diminish shear stress-evoked L-arginine uptake correlated with the extent of glycation (R2 = 0.88). Moreover, dLDL, but not nLDL or fraction alpha, reduced shear stress-mediated cGMP formation and NOx production by 47 and 88%, respectively. This effect was also mimicked by in vitro-glycated LDL, correlating with its degree of glycation (R2 = 0.86). Under these experimental conditions, glycated LDL reduced shear stress-induced increase in NO synthesis by inhibition of shear stress-stimulated L-arginine uptake and NO bioactivity due to increased endothelial cell *O2- release. These properties may contribute to the reduced vasodilatory response and the vascular complications in diabetes.

Adult↗
PubMed1998

Stealth ryanodine-sensitive Ca2+ release contributes to activity of capacitative Ca2+ entry and nitric oxide synthase in bovine endothelial cells.

1. The involvement of ryanodine-sensitive Ca2+ release (RsCR) in bradykinin (Bk)-induced Ca2+ release, capacitative Ca2+ entry (CCE) and nitric oxide synthase (NOS) activation was assessed in freshly isolated bovine coronary artery endothelial cells. 2. Using deconvolution microscopy fura-2 was found throughout the whole cytosol, while the cell membrane impermeable dye FFP-18 was exclusively in the cell membrane. Thus, perinuclear ([Ca2+]pn) and subplasmalemmal Ca2+ concentration ([Ca2+]sp) were monitored using fura-2 and FFP-18. 3. Inhibition of Na+-Ca2+ exchange by lowering extracellular Na+ concentration augmented the Bk-induced [Ca2+]pn signal in Ca2+-free solution. This effect was abolished when RsCR was prevented with 25 micromol l-1 ryanodine, while inhibition of RsCR had no effect on Bk-induced increase in [Ca2+]pn without inhibition of Na+-Ca2+ exchange. 4. Initiating RsCR by 200 nmol l-1 ryanodine increased [Ca2+]sp, while [Ca2+]pn remained constant. However, when Na+-Ca2+ exchange was prevented, ryanodine was also able to elevate [Ca2+]pn. 5. Blockage of RsCR diminished Ca2+ extrusion in response to stimulation with Bk in normal Na+-containing solution. 6. Inhibition of RsCR blunted Bk-activated CCE, while inhibition of Na+-Ca2+ exchange during stimulation enhanced CCE. 7. Although direct activation of RsCR failed to activate NOS, inhibition of RsCR diminished the effect of ATP and Bk on NOS, while the effect of thapsigargin remained unchanged. 8. These data suggest that during stimulation subplasmalemmal RsCR occurs, which contributes to the activities of CCE and NOS. Thus, the function of the subplasmalemmal Ca2+ control unit must be extended as a regulator for CCE and NOS.

Animals↗
PubMed1997

Vascular effects of L-arginine: anything beyond a substrate for the NO-synthase?

L-arginine supplementation is hypothesized to reduce endothelial dysfunction and atherogenesis via increased biosynthesis of nitric oxide. Here we describe superoxide scavenging properties of arginine as an additional aspect which needs to be considered. Furthermore, arginine reduced copper-induced lipid peroxidation, indicating that superoxide anions essentially contribute to this process. In intact endothelial cells, L-arginine but not D-arginine diminished superoxide release and reduced cell-mediated breakdown of nitric oxide. Our data indicate that the reported vascular effects of L-arginine supplementation might involve an increased bioavailability of nitric oxide due to its superoxide scavenging properties beside a potential increased NO biosynthesis.

Animals↗
PubMed1997

Role of superoxide anions in changes of endothelial vasoactive response during acute hyperglycemia.

The effects of acute hyperglycemia on endothelial Ca2+ signaling, formation of endothelium-derived relaxing factor (EDRF) and bioactivity of EDRF were investigated. Hyperglycemia increased 2,5-tert-butyl-1,4-hydrochinone (BHQ)-initiated Ca2+ signaling and EDRF formation in a concentration-dependent manner. The effect of elevated D-glucose on Ca2+/EDRF response could be diminished by co-incubation with the antioxidants vitamin E, probucol, GSH, vitamin C and superoxide dismutase. Convincingly, hyperglycemic conditions yielded an increase in superoxide anion release from endothelial cells and the superoxide anion-generating mixture xanthine oxidase/hypoxanthine mimicked the effect of hyperglycemia on Ca2+/EDRF signaling. Besides an enhanced formation of the vasodilatatory NO compound EDRF, hyperglycemia enhanced NO degradation by endothelial cells and, thus, reduced bioactivity of EDRF. We suggest that vasoactivity during acute hyperglycemia depends on the superoxide anion scavenging properties of the vascular wall. In acute hyperglycemia and early stages of diabetes, radical scavenging capacity may be suitable to protect NO degradation, resulting in an enhanced vasodilation. In contrast, decreased free radical scavenging properties of the vasculature in prolonged hyperglycemia and in later stages of diabetes might promote NO degradation by an overshoot of superoxide anions, resulting in an attenuation of endothelium-dependent vasodilation.

Animals↗