Biomedical subjects

S L Westbrook

Publications and source records attributed to S L Westbrook.

4 recordsLinked to original sources

PubMed1991

Alcohol-induced inhibition of N-methyl-D-aspartate-evoked release of [3H]norepinephrine from brain is related to lipophilicity.

A series of short chain alkanols were studied for their effects on N-methyl-D-aspartate (NMDA)-evoked release [3H]norepinephrine (NE) from slices of cortex of the rat. Methanol, ethanol, isopropanol, n-propanol, n-butanol and isoamyl alcohol inhibited NMDA-stimulated release of [3H]NE in a concentration-dependent manner, while having no effect on non-stimulated release of [3H]NE. The inhibitory potencies of the alkanols varied with the shorter chain alkanols, such as methanol, being less potent than the longer chain alkanols, such as isoamyl alcohol. Direct comparison of the effects of 100 mM methanol, ethanol, isopropanol, n-propanol and n-butanol indicated that increasing the chain length led to a greater efficacy for producing inhibition of NMDA-stimulated release of [3H]NE. A plot of the log IC50 values, versus the log of the membrane/buffer partition coefficients for the various alkanols was linear, indicating that lipophilicity played some role in the inhibitory effect. The alkanols did not significantly depress the release of [3H]NE stimulated by 25 mM KCl, in the presence of 300 microM 2-amino-5-phosphonopentanoic acid (AP-5), suggesting that the alkanols have a selective effect at the NMDA receptor, as opposed to altering the release of neurotransmitter at the nerve terminal. The inhibitory effects of the alcohols were reversible, which suggests that the alcohols were not causing non-specific toxic effects on the slices. It is concluded that the inhibitory effect of ethanol and related short chain alkanols on NMDA-stimulated release of [3H]NE involves an interaction with a lipophilic target, at or near the NMDA receptor-ionophore complex.

Alcohols↗

PubMed1988

Glucose transport in osteoblast-enriched bone explants: characterization and insulin regulation.

Insulin has potent effects on osteoblast function both in vivo and in vitro. In various insulin-sensitive tissues, stimulation of glucose transport and metabolism are hallmarks of insulin action, and have been postulated to play a role in insulin regulation of cellular function. However, insulin effects on glucose metabolism in osteoblast-like cells have not been demonstrated. Therefore we examined the in vitro effects of insulin on hexose uptake in an osteoblast-enriched rat bone explant preparation. Uniform 5-mm-diameter punch sections were obtained from the cartilage-free frontal portions of the calvaria of 3-day-old rats, and the periosteum was removed. The resulting sections contained a highly enriched population of osteoblast-like cells as determined by histologic criteria, elimination of calcitonin-stimulatable cAMP generation, and enhancement of PTH-stimulatable cAMP generation per microgram of DNA. Sections were incubated for 24 hr at 37 degrees C in BGJb medium and then transferred to modified glucose-free Krebs-Ringer bicarbonate buffer for 2-deoxy-D-glucose (2-DG) uptake studies. 3H-2-DG uptake was linear with time over 60 min, temperature sensitive, and inhibited by 5 mM phloridzin. Kinetic analysis of 2-DG uptake at 25 degrees C demonstrated a saturable transport mechanism with a Km of 2.2 mM, similar to that observed for 2-DG transport in other tissues. Studies of competitive inhibition by other sugars demonstrated a transport specificity for 2-DG that was comparable to that previously observed in fat and muscle cells.(ABSTRACT TRUNCATED AT 250 WORDS)

1-Methyl-3-isobutylxanthine↗

PubMed1987

Cytoplasmic pH regulation in canine renal proximal tubule cells.

The precise mechanisms by which the mammalian kidney proximal tubule transports H+ and HCO3- and regulates cytosolic pH (pHi) remain in doubt, though both a H+-ATPase pump and Na+/H+ exchange at the luminal membrane are known to function in the export of protons. The mechanisms of HCO3- transport are less clear though recent reports suggest an important role for an electrogenic Na+/HCO3- symport in the basolateral membrane. The importance of chloride-dependent bicarbonate transport is unknown. In the present studies, the pH-sensitive fluorescent dye, bis-(carboxyethyl)-carboxyfluorescein (BCECF) has been used to study pHi changes in suspensions of canine proximal tubule cells following acidification or alkalinization of the cytosol. Cells were acid-loaded to pH 6.5 by exposure to the H+/K+ ionophore, nigericin. Following removal of nigericin, pHi returned to basal levels (pHi = 7.1) when the cells were resuspended in a buffer containing 100 mM Na+. This recovery was blocked by removal of Na+ or addition of 0.2 mM amiloride to the cell suspension. In the presence of 0.2 mM amiloride and Na+, partial excretion of the acid load occurred if the buffer also contained HCO3-/CO2, but this effect was blocked by the removal of Na+ or the addition of 1 mM 4-acetomido-4'-isothiocyano-2,2'-stilbene disulfonic acid (SITS). When cell membrane potential was monitored in these experiments using the potential-sensitive fluorescent dye, bis-(1,3-dibutylbarbiturate) trimethine oxonol, the increase in pHi seen in the presence of Na+ was found to be electroneutral, whereas when that occurred in the presence of Na+, amiloride and HCO3-/CO2 was associated with membrane hyperpolarization.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗

PubMedDate not supplied

N-methyl-D-aspartate mediated responses decrease with age in Fischer 344 rat brain.

N-Methyl-D-aspartate (NMDA) receptor-mediated responses were studied in hippocampus, cortex, and striatum of Fischer 344 rats of various ages (3-5, 12-14, or 24-28 months old; young, middle-aged, and senescent or old, respectively) to determine whether aging alters the function of NMDA receptors. NMDA-induced inhibition of muscarinic-stimulated phosphoinositide hydrolysis in hippocampus, and NMDA-stimulated release of [3H]norepinephrine (NE) or [3H]dopamine (DA) were used as indices of NMDA receptor function. The muscarinic agonist carbachol (1 mM) stimulated PI hydrolysis in hippocampi from all three age groups with no significant differences between the groups. NMDA inhibited the carbachol-evoked PI response in a concentration-dependent manner (10-100 microM) in all age groups. However, the NMDA-induced (100 microM) inhibition of the carbachol-stimulated response was markedly reduced in an age-dependent manner with losses of 25% and 53% in middle-aged and senescent rats compared to young. Concentration-effect curves for NMDA-stimulated [3H]NE release were determined using hippocampal and cortical slices from rats of the three age groups. In the hippocampus the maximal response for NMDA was significantly decreased from 6.55 fractional [3H]NE release in young to 4.51 and 4.18 in middle-aged and old rats, respectively, with no age-related changes in the potency of NMDA or slope of the curves. In cortical slices the maximal response was significantly reduced in an age-dependent manner by 23% in the senescent rats compared to the young rats. NMDA-stimulated [3H]DA release from striatal slices was significantly lower in the senescent rats at concentrations of NMDA from 500-2000 microM.(ABSTRACT TRUNCATED AT 250 WORDS)

Aging↗