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S Barnes

Publications and source records attributed to S Barnes.

At least 19 recordsLinked to original sources
PubMed1992

Low-voltage-activated calcium channels in human retinoblastoma cells.

Retinoblastoma cells represent pluripotent neural-progenitor cells which, if induced to differentiate, express many features of mature human retinal neurons. Ca channel currents were recorded from isolated, undifferentiated human retinoblastoma Y79 cells in a bath solution containing 20 mM BaCl2 using whole-cell patch-clamp pipettes containing CsCl. The transient, macroscopic currents inactivated with a time constant of about 20 ms at -20 mV and had other properties similar to low-voltage-activated calcium channels described in other cell types: Activation curves fit by the Boltzmann relation had a midpoint of -32 mV and a slope factor of 6.8 mV (-80 mV holding potential) and inactivation curves had a midpoint of -40 mV and a slope factor of 3.7 mV. Non-stationary fluctuation analysis of the currents performed over a 2 kHz bandwidth indicated that each channel contributed 0.44 pA to the macroscopic transient current at -20 mV, suggesting a unitary conductance of about 7 pS.

Calcium Channels↗
PubMed1992

Auditing audits.

Explore the source record for details and available documents.

England↗
PubMed1992

Bioactivation of 7-hydroxymethyl-12-methylbenz[a]anthracene by rat liver bile acid sulfotransferase I.

The bioactivation of 7-hydroxymethyl-12-methylbenz[a]anthracene (HMBA) to an electrophilic sulfuric acid ester metabolite has been shown to be catalyzed by rat liver bile acid sulfotransferase I (BAST I). The sulfation and activation of HMBA by BAST I was determined by the ability of sulfated HMBA to form DNA adducts. The BAST I was also shown to react with rabbit anti-human dehydroepiandrosterone sulfotransferase antisera and to represent a major form of hydroxysteroid/bile acid sulfotransferase in female rat liver cytosol. Higher levels of BAST I activity and immunoreactivity as well as HMBA-DNA adduct formation were detected in female rat liver cytosol than in male rat liver cytosol. The bioactivation of HMBA by pure BAST I was dependent on the presence of 3'-phosphoadenosine 5'-phosphosulfate (PAPS) in the reaction and was inhibited by dehydroepiandrosterone, a physiological substrate for BAST I. Glutathione, a cellular nucleophile with important protective properties, decreased DNA adduct formation in the HMBA sulfation reaction in the absence of glutathione S-transferase activity. These results indicate the usefulness of BAST I to investigate the sulfation and activation of HMBA and probably other hydroxymethylated polyaromatic hydrocarbons to electrophilic and mutagenic metabolites under defined reaction conditions.

9,10-Dimethyl-1,2-benzanthracene↗
PubMed1992

Differential intestinal deconjugation of taurine and glycine bile acid N-acyl amidates in rats.

Mechanisms responsible for the difference in the relative amounts of taurine- and glycine-conjugated bile acid N-acyl amidates (Tau/Gly ratio) are not fully understood. In the present study, the stability of taurine- and glycine-conjugated bile acid N-acyl amidates during intestinal transit and absorption was examined to investigate the contribution of intestinal deconjugation to the Tau/Gly ratio in rat bile. Radiolabeled chenodeoxycholic acid (CDC) and its N-acyl amidates with glycine (CDC-Gly) or taurine (CDC-Tau) were introduced into the lumen of the upper small intestine in the biliary fistula rats, and radioactive metabolites in bile, blood, urine, and tissues were identified and quantitated by high-performance liquid chromatography. Results indicated that 1) extensive deconjugation of CDC-Gly occurs during intestinal absorption; 2) CDC-Tau is recovered in bile largely intact; and 3) newly synthesized CDC-Tau and CDC-Gly are formed in a ratio of less than 2:1 after administration of [14C]-CDC. In summary, the present study demonstrates that resistance of taurine-conjugated bile acid N-acyl amidates to hydrolysis in the intestine, rather than a difference in synthesis of taurine- and glycine-conjugated N-acyl amidates in liver, may account for the high Tau/Gly ratio in rat bile.

Animals↗
PubMed1992

Contribution of Ca and Ca-activated Cl channels to regenerative depolarization and membrane bistability of cone photoreceptors.

1. Cone photoreceptors in several vertebrate species generate Ca-dependent regenerative depolarizations (e.g., Ca spikes lasting up to 2 s) in response to current injection or surround illumination and may remain in a state of prolonged depolarization (e.g., a permanent plateau near 0 mV) after these stimuli. This paper, while confirming the role of Ca channels in the regenerative depolarization, demonstrates that Ca-activated Cl channels either enhance or hinder prolonged depolarization, depending on the value of the chloride equilibrium potential (ECl). 2. Current- and voltage-clamp recordings obtained with the whole-cell patch-clamp technique were compared in 158 isolated tiger salamander cones to determine the contribution of specific ion channel types to the two forms of depolarizing response. Cones dialyzed with CsCl or KCl intracellular solution (such that ECl = 0 mV) that had sustained negative slope regions in their current-voltage (I-V) relations recorded under voltage clamp, were, under current clamp, bistable with respect to their resting potential. Injection of approximately 20-pA steps of depolarizing current resulted in transitions from the negative stable membrane potential (near -50 mV) to a long lasting plateau around 0 mV. Injection of 200-300 pA of hyperpolarizing current could then force a return to the negative stable resting potential, although once repolarization occurred, current injection had to be reduced or terminated to prevent damaging hyperpolarization of the cell. 3. The inward currents accounting for the negative slope region of the I-V relation were carried in Ca and Ca-activated Cl channels. Specific block of Ca-activated Cl current (ICl(Ca)) by 100 microM niflumic acid (NFA) eliminated the prolonged depolarization, even though the negative slope conductance region in the I-V persisted and the cone could still produce the briefer Ca-dependent regenerative depolarizations. Application of 100 microM Cd2+ blocked both forms of depolarization. 4. Substitution of Ba2+, which among other actions did not activate ICl(Ca), usually supported regenerative depolarizations of shortened duration, demonstrating the role of Ca channels in the initial phase of these responses. 5. A difference was observed in the regenerative depolarization when ECl was shifted away from 0 mV, where it had been in the experiments described above. With ECl set to -40 or -60 mV by reduction of [Cl-] in the pipette, steady-state membrane bistability was eliminated and prolonged depolarization did not occur. Under these conditions, application of the Cl channel blocker NFA showed that ICl(Ca) contributes to membrane hyperpolarization.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗
PubMed1992

Estrogen and progesterone receptor status of mammary carcinomas and correlation with clinical outcome in dogs.

Estrogen and progesterone receptors (ER, PR) were measured in cytosol fractions from 18 primary canine mammary carcinomas by use of biochemical assays. One or both receptors were detected (> 10 fmol/mg of cytosol protein) in 11 tumors: 5 ER and PR; 2 ER only; 4 PR only. Mean cytoplasmic receptor concentrations (fmol/mg of cytosol protein) were 22.8 +/- 2.9 (SEM) for ER and 51.0 +/- 10.3 for PR in tumors containing ER and PR, 28.8 +/- 12.1 for ER in tumors containing only ER and 13.2 +/- 1.5 for PR in tumors containing only PR. Estrogen or progesterone receptors or both were identified in 6 of 9 tubular adenocarcinomas, 4 of 5 papillary adenocarcinomas, and 1 of 1 squamous cell carcinoma. These receptors were not identified in solid carcinomas (n = 2) or a single spindle cell carcinoma. Although the number of cases was limited, survival times of dogs tended to be longest in those with tumors containing ER alone or in combination with PR, intermediate in those with tumors containing only PR, and shortest in those with tumors without ER or PR. A correlation was not apparent between receptor status and age, presence of ovaries, tumor size, or histologic classification of the tumor. In the analysis of this series, the extent of surgery (mastectomy of the involved gland vs unilateral or bilateral mastectomy) did not appear to influence the outcome of the disease, and metastasis to regional lymph nodes did not appear to be a reliable prognostic indicator.

Animals↗
PubMed1992

Clinical apnea as an early manifestation of Pneumocystis carinii pneumonia in an infant with perinatal HIV-1 infection.

This article describes the first case of Pneumocystis carinii pneumonia in a human immunodeficiency virus (HIV) seropositive infant in whom apnea was the earliest presenting clinical finding. Pediatricians treating infants with HIV infection need to be aware of this unusual clinical presentation of P carinii pneumonia to avoid a delay in diagnosis and management of this disease.

Apnea↗
PubMed1991

Identification of bile acid-CoA: amino acid N-acyltransferase in rat kidney.

A novel location of the bile-acid-conjugating enzyme bile acid-CoA:amino acid N-acyltransferase (BAT) has been discovered in the cytosolic fraction of rat kidney. Both taurine and glycine were utilized as substrates. Formation of bile acid N-acyl amidates was verified by h.p.l.c. by comparison with authentic standards and by specific hydrolysis using cholylglycine hydrolase. Immunoblot analysis using a human liver anti-BAT polyclonal antibody indicated that rat kidney BAT has the same molecular mass as rat liver BAT. These findings suggest that the kidney has a role in bile acid metabolism and physiology.

Acyltransferases↗
PubMed1991

Genistein inhibition of the growth of human breast cancer cells: independence from estrogen receptors and the multi-drug resistance gene.

The effect of isoflavones on the growth of the human breast carcinoma cell lines, MDA-468 (estrogen receptor negative), and MCF-7 and MCF-7-D-40 (estrogen receptor positive), has been examined. Genistein is a potent inhibitor of the growth of each cell line (IC50 values from 6.5 to 12.0 micrograms/ml), whereas biochanin A and daidzein are weaker growth inhibitors (IC50 values from 20 to 34 micrograms/ml). The isoflavone beta-glucosides, genistin and daidzin, have little effect on growth (IC50 values greater than 100 micrograms/ml). The presence of the estrogen receptor is not required for the isoflavones to inhibit tumor cell growth (MDA-468 vs MCF-7 cells). In addition, the effects of genistein and biochanin A are not attenuated by overexpression of the multi-drug resistance gene product (MCF-7-D40 vs MCF-7 cells).

Antineoplastic Agents↗
PubMed1991

Purification and characterization of bile acid-CoA:amino acid N-acyltransferase from human liver.

The bile acid-conjugating enzyme, bile acid-CoA: amino acid N-acyltransferase, was purified 480-fold from the soluble fraction of homogenized frozen human liver. Purification was accomplished by a combination of anion exchange chromatography, chromatofocusing, glycocholate-AH-Sepharose affinity chromatography, and high performance liquid chromatography (HPLC) gel filtration. Following purification, the reduced, denatured enzyme migrated as a single 50-kDa protein band by sodium dodecyl sulfate-polyacrylamide gel electrophoresis. A similar molecular mass was obtained for the native enzyme by HPLC gel filtration. Elution from the chromatofocusing column suggested an apparent isoelectric point of 6.0 (+/- 0.2). Using a rabbit polyclonal antibody raised against the purified enzyme, Western blot analysis using 100,000 x g human liver supernatant confirmed that the affinity-purified polyclonal antibody was specific for human liver bile acid-CoA:amino acid N-acyltransferase. The purified enzyme utilized glycine, taurine, and 2-fluoro-beta-alanine (a 5-fluorouracil catabolite), but not beta-alanine, as substrates. Kinetic studies revealed apparent Km values for taurine, 2-fluoro-beta-alanine, and glycine of 1.1, 2.2, and 5.8 mM, respectively, with corresponding Vmax values of 0.33, 0.19, and 0.77 mumol/min/mg protein. These data demonstrate that a single monomeric enzyme is responsible for the conjugation of bile acids with glycine or taurine in human liver.

Acyltransferases↗
PubMed1991

Disposition and metabolism of 2-fluoro-beta-alanine conjugates of bile acids following secretion into bile.

Since 2-fluoro-beta-alanine (FBAL) conjugates of bile acids (BA), the primary biliary metabolites of fluoropyrimidine (FP) drugs, have been suggested to be related to the hepatotoxicity which develops in patients receiving FP chemotherapy by intrahepatic arterial infusion (Proc. Natl. Acad. Sci. USA 84, 5439-5443, 1987), it was important to determine whether they undergo enterohepatic circulation and hence accumulate in the liver and biliary system. In initial studies, sensitivity of FBAL-BA conjugates to hydrolysis by pancreatic enzymes was examined. In subsequent in vivo studies, a model FBAL-BA conjugate, FBAL-chenodeoxycholate (FBAL-CDC), was introduced into the lumen of the small intestine of anesthetized rats with biliary fistulas to quantitate the intestinal absorption, metabolism and tissue distribution of the conjugate. The results indicated that: (1) FBAL-BA conjugates were resistant to hydrolysis by pancreatic enzymes (carboxypeptidase A, carboxypeptidase B and trypsin) and by human pancreatic juice, but were completely hydrolyzed by cholyglycine hydrolase. (2) At least one-half of the administered FBAL-CDC was deconjugated during the process of intestinal absorption, as shown by HPLC analysis of the radioactivity in portal venous blood. (3) Deconjugated FBAL or CDC was reconjugated in liver with other bile acids or amino acids (glycine and taurine), respectively, as shown by radiochromatography of bile. (4) FBAL, formed as a result of hydrolysis of FBAL-CDC, had a wide tissue distribution. In conclusion, FBAL-CDC has a rapid turnover during its enterohepatic circulation due to deconjugation in the intestine and reconjugation in the liver.

Animals↗
PubMed1991

A comparative study of bile acid CoA:amino acid:N-acyltransferase (BAT) from four mammalian species.

1. Bile acid CoA:amino acid:N-acyltransferase (BAT) was partially purified from dog, human, pig and rat livers. The interspecies variation in substrate specificity and kinetics were determined for glycine and taurine. 2. BAT activity from dog liver formed bile acid conjugates with taurine exclusively, whereas BAT activity from each of the other species formed conjugates with both taurine and glycine. 3. Biliary composition of glycine and taurine bile acid conjugates could partly be accounted for by substrate affinity (Km) and turnover number (Vmax) of BAT activity. 4. A monospecific anti-human BAT polyclonal antibody reacted on Western blot analysis with a 40 kDa band in a 100,000 g supernatant fraction from rat liver. 5. Immunoabsorption chromatography using an anti-human BAT antibody-Sepharose affinity column showed that both the immunoreactive protein band and BAT activity were removed from the 100,000 g supernatant fraction from human and rat livers.

Acetyltransferases↗
PubMed1991

Cholecystokinin modulates the release of dopamine from the anterior and posterior nucleus accumbens by two different mechanisms.

The effects of various cholecystokinin (CCK)-related peptides were investigated on 35 mM K(+)-stimulated endogenous dopamine release from slices of either anterior or posterior nucleus accumbens of the rat. CCK sulphated octapeptide (1-10 microM), but not pentagastrin or CCK unsulphated octapeptide, was found to cause a dose-dependent increase in the release from the posterior nucleus accumbens. This effect was blocked by low doses of the CCKA receptor antagonist L364,718 (10 nM) but not the CCKB receptor antagonist L365,260. In the anterior nucleus accumbens CCK sulphated octapeptide (1 microM) and CCK unsulphated octapeptide (0.1-1 microM) inhibited the dopamine release, and this effect was blocked by L365,260 (10-100 nM) but not by L364,718. These results suggest that CCK has a different effect on dopamine release from the anterior and posterior nucleus accumbens and that these effects are mediated by two different types of CCK receptor.

Animals↗
PubMed1991

Effect of cholecystokinin octapeptide on endogenous amino acid release from the rat ventromedial nucleus of the hypothalamus and striatum.

The sulphated octapeptide of cholecystokinin (CCK-8S) was found to cause a dose-dependent increase in the basal release of aspartate, glycine, and gamma-aminobutyric acid from the striatum and the ventromedial nucleus of the hypothalamus (VMH). No effect on amino acid release was observed after electrical (VMH) or potassium (striatum) stimulation. Experiments performed using the CCKB-selective antagonist L-365,260 and the CCKA-selective antagonist L-364,718 suggested that this action of CCK-8S was mediated via the CCKB receptor. The ability of CCK-8S to evoke amino acid release was not dependent on the presence of extracellular calcium, though the effect was abolished by tetrodotoxin. Inhibition of protein kinase activity by staurosporine prevented the excitatory effects of CCK-8S on amino acid release.

Alkaloids↗