Carotid Artery Injection Technique: Bounds for Bolus Mixing by Plasma and by Brain

Estimation of Michaelis-Menten kinetic parameters ( Km, Vmax) of blood–brain barrier (BBB) transport processes with the carotid artery single injection technique assumes that mixing of the bolus with unlabeled substrate either from (a) circulating plasma or (b) amino acid efflux from brain, is minimal. The maximum extent to which the bolus could mix by these two sources is quantified in the present studies by measuring 14C-phenylalanine extraction in pentobarbital-anesthetized and conscious rats after the addition of 0–80% rat serum to the arterial injection solution. An upper bound (±SE) of bolus mixing due to mixing from both sources, expressed in terms of percentage of rat plasma, is 8.8 ± 1.9 and 7.0 ± 2.1% for the anesthetized and conscious rat, respectively. The estimated contribution to bolus mixing due to amino acid efflux from brain is 3.3 and 2.1% for the anesthetized and conscious rat, respectively. Based on these estimates, the upper bound for bolus mixing with circulating rat plasma is only 5.5 and 4.9%, respectively, for the anesthetized and conscious catheterized rat. Thus, any bolus mixing after rapid carotid injection is relatively small and is comparable to the mixing effects observed with the carotid artery infusion technique. Mixing effects on the order of 5% are shown to have no significant effect on the estimation of kinetic parameters of BBB nutrient transport, except for neutral and basic amino acid transport, which are characterized by very low Km values relative to the usual amino acid plasma concentrations. In the rat, a 5% mixing results in an enrichment of the bolus concentration of unlabeled amino acid that approximates the Km of the transport process, and this results in an overestimation of the absolute Km value. However, mixing effects are shown to have little, if any, impact on the estimation of the transport Vmax, KD, or apparent Km. Thus, amino acid influx rates predicted from kinetic constants obtained with the carotid injection technique are reliable, even if bolus mixing effects with the carotid injection technique are as high as 7–9%.

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Ideal and nonideal mixing effects of amino acid based-surfactant on interfacial rheology and foam properties

Korea-Australia Rheology Journal ◽

10.1007/s13367-021-0010-4 ◽

2021 ◽

Vol 33 (2) ◽

pp. 113-122

Author(s):

Jung-Eun Bae ◽

Kyunghwan Kim ◽

Nae-Gyu Kang

Keyword(s):

Amino Acid ◽

Interfacial Rheology ◽

Mixing Effects ◽

Foam Properties

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A synthetic glucagon-like peptide-1 analog with improved plasma stability

Journal of Endocrinology ◽

10.1677/joe.0.1590093 ◽

1998 ◽

Vol 159 (1) ◽

pp. 93-102 ◽

Cited By ~ 44

Author(s):

U Ritzel ◽

U Leonhardt ◽

M Ottleben ◽

A Ruhmann ◽

K Eckart ◽

...

Keyword(s):

Amino Acid ◽

Plasma Insulin ◽

Rat Plasma ◽

Plasma Stability ◽

Terminal Amino Acid ◽

Terminal Amino ◽

Glucagon Like Peptide ◽

Glucagon Like Peptide 1

Glucagon-like peptide-1 (GLP-1) is the most potent endogenous insulin-stimulating hormone. In the present study the plasma stability and biological activity of a GLP-1 analog, [Ser]GLP-1(7-36)amide, in which the second N-terminal amino acid alanine was replaced by serine, was evaluated in vitro and in vivo. Incubation of GLP-1 with human or rat plasma resulted in degradation of native GLP-1(7-36)amide to GLP-1(9-36)amide, while [Ser]GLP-1(7-36)amide was not significantly degraded by plasma enzymes. Using glucose-responsive HIT-T15 cells, [Ser]GLP-1(7-36)amide showed strong insulinotropic activity, which was inhibited by the specific GLP-1 receptor antagonist exendin-4(9-39)amide. Simultaneous i.v. injection of [Ser]GLP-1(7-36)amide and glucose in rats induced a twofold higher increase in plasma insulin levels than unmodified GLP-1(7-36)amide with glucose and a fivefold higher increase than glucose alone. [Ser]GLP-1(7-36)amide induced a 1.5-fold higher increase in plasma insulin than GLP-1(7-36)amide when given 1 h before i.v. application of glucose. The insulinotropic effect of [Ser]GLP-1(7-36)amide was suppressed by i.v. application of exendin-4(9-39)amide. The present data demonstrate that replacement of the second N-terminal amino acid alanine by serine improves the plasma stability of GLP-1(7-36)amide. The insulinotropic action in vitro and in vivo was not impaired significantly by this modification.

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Multiple components of arginine and phenylalanine transport induced in neutral and basic amino acid transporter-cRNA-injected Xenopus oocytes

Biochemical Journal ◽

10.1042/bj3180915 ◽

1996 ◽

Vol 318 (3) ◽

pp. 915-922 ◽

Cited By ~ 13

Author(s):

George J PETER ◽

Iain G. DAVIDSON ◽

Aamir AHMED ◽

Lynn McILROY ◽

Alexander R. FORRESTER ◽

...

Keyword(s):

Amino Acid ◽

Xenopus Oocytes ◽

Competitive Inhibition ◽

Protein Complexes ◽

Basic Amino Acid ◽

Amino Acid Transporter ◽

Transport Processes ◽

Arginine Transport ◽

Acid Transporter ◽

Phenylalanine Transport

The induced uptakes of l-[3H]phenylalanine and l-[3H]arginine in oocytes injected with clonal NBAT (neutral and basic amino acid transporter) cRNA show differential inactivation by pre-treatment with N-ethylmaleimide (NEM), revealing at least two distinct transport processes. NEM-resistant arginine transport is inhibited by leucine and phenylalanine but not by alanine or valine; mutual competitive inhibition of NEM-resistant uptake of arginine and phenylalanine indicates that the two amino acids share a single transporter. NEM-senstive arginine transport is inhibited by leucine, phenylalanine, alanine and valine. At least two NEM-sensitive transporters may be expressed because we have been unable to confirm mutual competitive inhibition between arginine and phenylalanine transport. The NEM-resistant transport mechanism appears to involve distinct but overlapping binding sites for cationic and zwitterionic substrates. NBAT is known to form oligomeric protein complexes in cell membranes, and its functional roles when expressed in Xenopus oocytes may include interaction with oocyte proteins, leading to increased native amino acid transport activities; these resemble NBAT-expressed activities in terms of NEM-sensitivity and apparent substrate range (including an unusual inhibition by β-phenylalanine).

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Effect of Essential Amino Acid Deficiency on Lecithin - Cholesterol Acyltransferase in Rat Plasma : Dietary Factors Influencing Lecithin - Cholestetol Acyltransferase in Rat Plasma (Part 3)

Journal of the Faculty of Agriculture, Kyushu University ◽

10.5109/22858 ◽

1974 ◽

Vol 18 (3) ◽

pp. 207-220

Author(s):

Kohji Hori ◽

Shuji Fujita ◽

Kuo-Yu Ho ◽

Michihiro Sugano

Keyword(s):

Amino Acid ◽

Essential Amino Acid ◽

Cholesterol Acyltransferase ◽

Rat Plasma ◽

Dietary Factors ◽

Amino Acid Deficiency ◽

Lecithin Cholesterol Acyltransferase ◽

Factors Influencing ◽

Acid Deficiency

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Effect of serum proteins on sodium-linked transport processes in cultured kidney cells.

Journal of the American Society of Nephrology ◽

10.1681/asn.v5111964 ◽

1995 ◽

Vol 5 (11) ◽

pp. 1964-1970

Author(s):

S S Blumenthal ◽

D L Lewand ◽

P A Tipnis ◽

J G Kleinman

Keyword(s):

Amino Acid ◽

Dextran Sulfate ◽

Cultured Cells ◽

Serum Proteins ◽

Fluid Phase ◽

Defined Medium ◽

Transport Processes ◽

Transport Systems ◽

Heat Treated ◽

Fluid Phase Endocytosis

The mechanism for increased Na+ retention in the nephrotic syndrome is unknown. To determine if Na+ transport systems in the proximal tubule might be affected by filtered proteins, mouse cortical tubule cells grown in defined medium were exposed to concentrations of bovine serum albumin (BSA) ranging from 0.01 to 0.5%. Activity of the Na(+)-glucose cotransporter, measured as Na(+)-dependent uptake of alpha-methylglucoside, increased progressively to a maximum of 2.3-fold above baseline (P < 0.001; N = 10). The increase in transporter activity was due to an increased Vmax, and the magnitude of the increase was inversely related to the basal cotransporter activity of the cultures. Increased cotransporter activity was detectable 6 h after exposure, was sustained for 24 h after cells were removed from an albumin-free medium, and was prevented by cycloheximide. Heat-treated BSA, fatty-acid and globulin-free BSA, and gamma-globulins were as effective at increasing Na(+)-glucose cotransporter activity as untreated Fraction V BSA. Dextran, dextran-sulfate, and amino acid supplements were ineffective. Neither protease inhibitors nor chloroquine added to an albumin-containing medium prevented increased alpha-methylglucoside uptake. Albumin did not change the rate of fluid-phase endocytosis in the cultured cells. Na(+)-amino acid cotransport and Na(+)-H+ exchange were either decreased or unchanged after BSA exposure. Exposing apical surfaces of cells grown on permeable membranes to BSA led to a greater increase in activity of the Na(+)-glucose cotransporter relative to controls than did exposing the basolateral surface (145 versus 89%; P < 0.05; N = 5).(ABSTRACT TRUNCATED AT 250 WORDS)

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