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Cationic amino acid (CAA) transport is brought about by two families of proteins that are found in various tissues: Cat (CAA transporter), referred to as system [y.sup.+], and Bat [broad-scope amino acid (AA) transporter], which comprises systems [b.sup.0,+], [B.sup.0,+], and [y.sup.+]L. CAA traverse the blood-brain barrier (BBB), but experiments done in vivo have only been able to examine the BBB from the luminal (blood-facing) side. In the present study, plasma membranes isolated from bovine brain microvessels were used to identify and characterize the CAA transporter(s) on both sides of the BBB. From these studies, it was concluded that system [y.sup.+] was the only transporter present, with a prevalence of activity on the abluminal membrane. System [y.sup.+] was voltage dependent and had a [K.sub.m] of 470 [+ or -] 106 [micro]M (SE) for lysine, a [K.sub.i] of 34 [micro]M for arginine, and a [K.sub.i] of 290 [micro]M for omithine. In the presence of [Na.sup.+], system y + was inhibited by several essential neutral AAs. The [K.sub.i] values were 3-10 times the plasma concentrations, suggesting that system [y.sup.+] was not as important a point of access for these AAs as system L1. Several small nonessential AAs (serine, glutamine, alanine,and glycine) inhibited system [y.sup.+] with [K.sub.i] values similar to their plasma concentrations, suggesting that system [y.sup.+] may account for the permeability of the BBB to these AAs. System [y.sup.+] may be important in the provision of arginine for NO synthesis. Real-time PCR and Western blotting techniques established the presence of the three known nitric oxide synthases in cerebral endothelial cells: NOS-1 (neuronal), NOS-2 (inducible), and NOS-3 (endothelial). These results confirm that system [y.sup.+] is the only CAA transporter in the BBB and suggest that NO can be produced in brain endothelial cells. amino acid active transport; brain capillaries; endothelial cells; essential amino acids; nonessential amino acids; polarity doi:10.1152/ajpendo.00007.2006

Brain capillary endothelial cells form the blood-brain barrier (BBB). They are connected by extensive tight junctions, and are polarized into luminal (blood-facing) and abluminal (brain-facing) plasma membrane domains. The polar distribution of transport proteins mediates amino acid (AA) homeostasis in the brain. The existence of two facilitative transporters for neutral amino acids (NAAs) on both membranes provides the brain access to essential AAs. Four [Na.sup.+]-dependent transporters of NAA exist in the abluminal membranes of the BBB. Together these systems have the capability to actively transfer every naturally occurring NAA from the extracellular fluid (ECF) to endothelial cells and from there into circulation. The presence of [Na.sup.+]-dependent carriers on the abluminal membrane provides a mechanism by which NAA concentrations in the ECF of brain are maintained at ~10% those of the plasma. Also present on the abluminal membrane are at least three [Na.sup.+]-dependent systems transporting acidic AAs (EAAT) and a [Na.sup.+]-dependent system transporting glutamine (N). Facilitative carriers for glutamine and glutamate are found only in the luminal membrane of the BBB. This organization promotes the net removal of acidic- and nitrogen-rich AAs from the brain and accounts for the low level of glutamate penetration into the central nervous system. The presence of a [gamma]-glutamyl cycle at the luminal membrane and [Na.sup.+]-dependent AA transporters at the abluminal membrane may serve to modulate movement of AAs from blood to the brain. The [gamma]-glutamyl cycle is expected to generate pyroglutamate (synonymous with oxyproline) within the endothelial cells. Pyroglutamate stimulates secondary active AA transporters at the abluminal membrane, thereby reducing the net influx of AAs to the brain. It is now clear that BBB participates in the active regulation of the AA content of the brain. KEY WORDS: * brain capillaries * endothelial cells * polarity * sodium dependent transport * facilitative transport

[Na.sup.+] -dependent neutral amino acid transporters A, ASC, and N of the blood-brain barrier: mechanisms for neutral amino acid removal. Am J Physiol Endocrinol Metab :287: E622-E629, 2004. First published May 27, 2004; 10.1152/ajpendo.00187.2004.--Four [Na.sup.+]-dependent transporters of neutral amino acids (NAA) are known to exist in the abluminal membranes (brain side) of the blood-brain barrier (BBB). This article describes the kinetic characteristics of systems A, ASC, and N that, together with the recently described [Na.sup.+]-dependent system for large NAA ([Na.sup.+]-LNAA), provide a basis for understanding the functional organization of the BBB. The data demonstrate that system A is voltage dependent (3 positive charges accompany each molecule of substrate). Systems ASC and N are not voltage dependent. Each NAA is a putative substrate for at least one system, and several NAA are transported by as many as three. System A transports Pro, Ala, His, Ash, Ser, and Gin; system ASC transports Ser, Gly, Met, Val, Leu, Ile, Cys, and Thr; system N transports Gin, His, Set, and Asn; [Na.sup.+]-LNAA transports Leu, Ile, Val, Trp, Tyr, Phe, Met, Ala, His, Thr, and Gly. Together, these four systems have the capability to actively transfer every naturally occurring NAA from the extracellular fluid (ECF) to endothelial cells and thence to the circulation. The existence of facilitative transport for NAA (L1) on both membranes provides the brain access to essential NAA. The presence of [Na.sup.+]-dependent carriers on the abluminal membrane provides a mechanism by which NAA concentrations in the ECF of brain are maintained at ~10% of those of the plasma. active transport; brain extracellular fluid; capillaries; endothelial cells; essential amino acids

Liver 7-cystathionase activity increases in rats during lactation; its inhibition due to propargylglycine is followed by a significant decrease in lactation. This is reversible by N-acetylcysteine administration. To study the role of liver [Gamma]-cystathionase and the intertissue flux of glutathione during lactation, we used lactating and virgin rats fed liquid diets. Virgin rats were divided into two groups as follows: one group was fed daily a diet containing the same amount of protein that was consumed the previous day by lactating rats (high protein diet-fed rats); the other virgin group was fed the normal liquid diet (control). The expression and activity of liver [Gamma]-cystathionase were significantly greater in lactating rats and in high protein diet-fed virgin rats compared with control rats. The total glutathione [reduced glutathione (GSH) + oxidized glutathione (GSSG)] released per gram of liver did not differ in lactating rats or in high protein diet-fed rats, but it was significantly higher in these two groups than in control virgin rats. Liver size and the GSH + GSSG released by total liver were significantly higher in lactating rats than in high protein diet-fed virgin rats, and this difference was similar to the amount of glutathione taken up by the mammary gland (454.2 [+ or -] 36.0 nmol/min). The uptake of total glutathione by the lactating mammary gland was much higher than the uptakes of free L-cysteine and L-cystine, which were negligible. These data suggest that the intertissue flux of glutathione is an important mechanism of L-cysteine delivery to the lactating mammary gland, which lacks [Gamma]-cystathionase activity. This emphasizes the physiologic importance of the increased expression and activity of liver [Gamma]-cystathionase during lactation. KEY WORDS: L-cysteine; glutathione; lactating mammary gland; L-cystathionine; rats

Isolated plasma membrane vesicles from the luminal and abluminal side of bovine brain capillaries were examined to investigate the mechanism of nitrogen waste removal in the brain given the blood brain barrier. Results reveal that the capillaries in the brain are active participants in the removal of nitrogenous wastes from the brain in the form of glutamine, glutamate and ammonia.

To study the redistribution of amino acids to the mammary gland during lactation we used lactating and virgin rats fed liquid diets. Virgin rats were divided in two groups: one group was fed daily a diet containing the same amount of protein that was consumed the previous day by lactating rats (high protein diet-fed rats), and the other virgin group was fed the normal liquid diet (control). The hepatic availability of amino acids was significantly higher in the lactating rats than in the other two groups, but the uptake and fractional extraction of amino acids by the liver were lower in lactating rats than in the high protein-fed virgin controls. When primary hepatocyte cultures were used, the uptake of 2-amino-[1-14C]isobutyric acid (AIB) and the activity of system A were found to be significantly higher in the hepatocytes from virgin rats fed the high protein diet than in those obtained from the lactating and control virgin groups. No difference was observed between the control virgin rats and the lactating rats. The kinetics of AIB showed that the [V.sub.max]/[K.sub.m] ratio was significantly lower in hepatocytes from lactating rats than in those from the high protein diet-fed virgin rats. Addition of prolactin to the incubation medium decreased the uptake of AIB in hepatocytes from both groups of virgin rats. Moreover, uptake of AIB was greater in bromocriptine-treated lactating rats and in lactating rats that had had their pups removed for the preceding 24 h compared with values for the lactating rats. These data suggest that liver amino acid uptake is decreased during lactation, redistributing these amino acids from the liver to the lactating mammary gland, and that prolactin is a potential signal for this intertissue flux of amino acids. INDEXING KEY WORDS: liver; lactation; prolactin; amino acid uptake; rats

In this paper, an integrated double buck–boost (IDBB) converter is proposed as a high-power-factor offline power supply for power-LED lamps. The IDBB converter features just one controlled switch and two inductors and is able to supply a solid-state lamp from the mains, providing high power factor and good efficiency. In this paper, the IDBB converter is analyzed, and a design methodology is proposed. It is demonstrated that, with a careful design of the converter, the filter capacitances can be made small enough so that film capacitors may be used. In this way, the converter mean time between failures can be made as high as that of the solid-state lamp. A design example for a 70-W converter supplied from a 230 V/50 Hz mains for street lighting applications is shown. Finally, experimental results from a laboratory prototype are also presented. [ABSTRACT FROM AUTHOR]

Investigates whether glutamine transport by the blood-brain barrier is a possible mechanism for nitrogen removal. Separation of membrane vesicles; Facilitative transport of glutamine; Glutamate transport; Glutamine metabolism in the endothelial cells of the blood-brain barrier.