Biography:

In the past Bruce R. Stevens has collaborated on articles with Ernest M. Wright and Mark E. Mailliard. One of their most recent publications is BBA reportSpecificity of intestinal brush-border proline transport: cyanine dye studies. Which was published in journal Biochimica et Biophysica Acta (BBA) - Biomembranes.

More information about Bruce R. Stevens research including statistics on their citations can be found on their Copernicus Academic profile page.

Bruce R. Stevens's Articles: (10)

BBA reportSpecificity of intestinal brush-border proline transport: cyanine dye studies

AbstractThe ability of rabbit jejunal brush borders to transport inhibitors of the imino carrier was investigated in membrane vesicles by measuring their ability to depolarize the membrane potential. Membrane potentials were monitored using a voltage-sensitive cyanine dye. Piperidine and pyrrolidine carboxylic acids, which are potent inhibitors of Na+-dependent proline transport (Ki < 0.5 mM) depolarize the potential in a Na+-dependent, saturable manner indicating transport. On the other hand, N-methylated amino acids, which are fair inhibitors (Ki 2–10 mM), do not depolarize the membrane to any significant extent, but they competitively inhibit the l-proline transport signal. This indicates that these analogs are nontransported inhibitors of the imino carrier. The poor inhibitors niacin and pipolinic acid (Ki>60 mM) depolarize the membrane about twice as much as proline and with low Kf values. This suggests separate carriers for these substrates.

BBA reportSpecificity of intestinal brush-border proline transport: cyanine dye studies

AbstractThe ability of rabbit jejunal brush borders to transport inhibitors of the imino carrier was investigated in membrane vesicles by measuring their ability to depolarize the membrane potential. Membrane potentials were monitored using a voltage-sensitive cyanine dye. Piperidine and pyrrolidine carboxylic acids, which are potent inhibitors of Na+-dependent proline transport (Ki < 0.5 mM) depolarize the potential in a Na+-dependent, saturable manner indicating transport. On the other hand, N-methylated amino acids, which are fair inhibitors (Ki 2–10 mM), do not depolarize the membrane to any significant extent, but they competitively inhibit the l-proline transport signal. This indicates that these analogs are nontransported inhibitors of the imino carrier. The poor inhibitors niacin and pipolinic acid (Ki>60 mM) depolarize the membrane about twice as much as proline and with low Kf values. This suggests separate carriers for these substrates.

BBA reportSpecificity of intestinal brush-border proline transport: cyanine dye studies

AbstractThe ability of rabbit jejunal brush borders to transport inhibitors of the imino carrier was investigated in membrane vesicles by measuring their ability to depolarize the membrane potential. Membrane potentials were monitored using a voltage-sensitive cyanine dye. Piperidine and pyrrolidine carboxylic acids, which are potent inhibitors of Na+-dependent proline transport (Ki < 0.5 mM) depolarize the potential in a Na+-dependent, saturable manner indicating transport. On the other hand, N-methylated amino acids, which are fair inhibitors (Ki 2–10 mM), do not depolarize the membrane to any significant extent, but they competitively inhibit the l-proline transport signal. This indicates that these analogs are nontransported inhibitors of the imino carrier. The poor inhibitors niacin and pipolinic acid (Ki>60 mM) depolarize the membrane about twice as much as proline and with low Kf values. This suggests separate carriers for these substrates.

Human intestinal brush border angiotensin-converting enzyme activity and its inhibition by antihypertensive Ramipril

AbstractAngiotensin-converting enzyme (ACE) has been identified as a prominent brush border membrane-bound enzyme of human jejunum. In this study, we purified brush border membrane vesicles enriched in ACE, and characterized the ACE with regard to (a) its stability in the membrane, (b) substrate hydrolysis kinetics compared with pulmonary endothelial ACE, and (c) pharmacologic interaction with Ramipril. These investigations resulted in the following findings. The uninhibited enzyme is stable in native membranes in vitro, with a half-life of 195 ± 7 h. Kinetic analysis of ACE hydrolysis activity revealed the presence of a single enzyme species, which yielded a high Vmax and displayed a Km similar to purified ACE from lung endothelium. Brush border ACE was inhibited by Ramipril, one of the most specific and potent orally administered ACE inhibitors indicated for hypertension. We determined the brush border ACE value of IC50 = 3 × 10−9 M Ramipril-diacid, which is the same value for serum and lung ACE. Brush border ACE remains 100% inhibited by 10 μM Ramipril during at least 8 days in vitro. The data indicate that ACE is a prominent jejunal brush border enzyme that behaves pharmacologically and kinetically like its peripheral circulation counterpart. This study suggests that high doses of orally administered ACE inhibitors may affect intestinal epithelial function.

Dietary modulation of small intestinal glutamine transport in intestinal brush border membrane vesicles of rats

AbstractThe effects of a glutamine-enriched diet on the transport of glutamine across brush border membrane vesicles (BBMV) from the rat jejunum were studied to gain further insight into the effects of diet on regulating gut glutamine utilization. Following fasting, rats were randomized to one of three nutritionally complete elemental diets supplemented with glutamine, glutamate, or glycine (control). Brush border membrane vesicles were prepared by a Mg2+ aggregation/differential centrifugation technique and uptake of radioactive [3H]glutamine by the BBMV was studied using a rapid mixing/filtration technique. BBMVs from all test diet groups were enriched in alkaline phosphatase 14-fold. [3H]Glutamine uptake courses for all groups demonstrated sodium dependency, overshoots, and similar 2-hr equilibrium values. Vesicles from animals fed the glutamine-enriched diet had a 75% increase in glutamine uptake compared to those of the control diet and a 250% increase compared to those of the glutamate-enriched diet (P < 0.05). α-Methylamino isobutyric acid and glycine did not significantly inhibit total [3H]glutamine uptake, whereas asparagine and glutamine inhibited total [3H]glutamine uptake compared to the mannitol control. The brush border appears to possess the glutamine selective System N transporter, the activity of which can be stimulated by providing dietary glutamine.

Neonatal rat brain astroglial dipeptidyl peptidase II activity regulation by cations and anions

AbstractAstrocytic glial cells from neonatal rat brains were grown in primary culture. Dipeptidyl peptidase II (DPP-II) enzyme activity was measured in cells disrupted by nonionic detergent. The rate of enzyme activity was measured in the presence of various ions, under isosmotic conditions adjusted using mannitol and NaCl. DPP-II activity was not affected by the candidate metal co-factors (2 mM) Co2+, Mg2+, and Mn2+, nor by the metal chelators EDTA and o-phenanthroline. However, selected cations (50 mM Cl− salts) significantly inhibited DPP-II activity compared to Na+ control; the relative inhibition ranking was Rb+ < K+ < Zn2+ < Hg2+. Many test anions (50 mM Na+ salts) also inhibited DPP-II activity compared to Cl− control: SO42 < NO3− < F− < SO32−. Surprisingly, the anion S2O32− was the on strongly stimulated activity. The data are consistent with the concept that specific ion species interact with the glial DPP-II enzyme to affect catalytic activity.

Ramipril inhibition of rabbit (Oryctolagus cuniculus) small intestinal brush border membrane angiotensin converting enzyme

Abstract1.1. Rabbit small intestinal brush border membranes possessed prominent angiotensin converting enzyme (ACE) activity.2.2. Intestinal ACE was located on the lumen surface, as verified by ACE co-enrichment with brush border membrane marker enzymes.3.3. Hydrolysis kinetics of rabbit intestinal ACE were comparable to the lung, utilizing the substrate (N-[3-(2-furyl)acryloyl]-l-phenylalanylglycylglycine; the Vmax = 543 ± 51 μmol/min/g and Km = 0.62 ± 0.09 mmol/l.4.4. Intestinal brush border ACE activity was strongly inhibited by the antihypertensive drug Ramipril, which yielded an ic50 value of 5 nmol/l; the ACE activity remained completely inhibited during 15 days after a single dose of 10 μmol/l Ramipril.

Regular ArticleSodium-Dependent Amino Acid Transport Is Preserved in Lyophilized Reconstituted Apical Membranes from Intestinal Epithelium☆

AbstractWe demonstrate for the first time that functional electrogenic Na+-dependent amino acid transport is preserved for extended periods when purified brush border membranes prepared in hypotonic media are lyophilized and then rehydrated in buffer containing mannitol, NaSCN, and/or KSCN/valinomycin. Reconstituted lyophilized apical membranes from small intestine formed morphologically, physiologically, and thermodynamically normal vesicles which transportedl-alanine via system B into an osmotically active space energized by secondary active transport, as measured under equilibrium and nonequilibrium conditions. The lyophilized membranes are readily prepared and stored, thereby providing a means to pool large quantities of formed vesicles that are useful in examining cloned and reconstituted native amino acid transporter polypeptides.

Alpha-lipoic acid effects on brain glial functions accompanying double-stranded RNA antiviral and inflammatory signaling☆

Highlights•Lipoic acid (LA) averts untoward events of dsRNA-activated TLR3- and PKR-signaled glial dysfunction.•LA suppresses activated glial mRNA levels of IL-1β, IL-6, TNFα, CAT2, 4F2hc, xCT, PAMP genes, and iNOS.•LA augments IL-10, GLAST (but not GLT-1) and regulatory subunits of γ-glutamyl cysteine ligase..•Glial glutamate net uptake is inhibited by dsRNA, and this is relieved by LA.•LA protects against gliotoxicity, suggesting efficacy in dsRNA- or virus-induced CNS pathology.

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