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Biomedical subjects

J R Cooper

Publications and source records attributed to J R Cooper.

At least 73 records · Page 4Linked to original sources
PubMed1986

Isolation of a factor (substance B) that antagonizes presynaptic modulation: pharmacological properties.

An aqueous extract of brain has recently been shown to contain a factor (substance B) that antagonizes presynaptic inhibition of evoked [3H]acetylcholine release from guinea pig ileal synaptosomes. This factor antagonized the inhibition of electrically evoked contractions of the intact guinea pig longitudinal muscle-myenteric plexus preparation by a variety of pharmacological agents including clonidine, 2-chloroadenosine, morphine and phencyclidine. pA2App values for substance B antagonism of these four agonists were very similar. Schild plot analysis suggests a functional competition between substance B and each of these receptor agonists. In the absence of any agonist, substance B had a minimal effect on the force of contraction. This reversal of inhibition by substance B was not altered by the ganglionic blocking agent hexamethonium. Substance B was not able to reverse the inhibition of contractions elicited by atropine. In addition to its localization in brain, the factor was also found in appreciable quantities in the heart and the ileum, but not in the liver or kidney. These results indicate that an endogenous neuromodulator exists in innervated tissues that antagonizes a subcellular mechanism(s) involved in mediating inhibition of neurotransmitter release by alpha adrenergic, opiate and purinergic agonists, as well as phencyclidine.

2-Chloroadenosine↗
PubMed1985

Involvement of sulfhydryl groups in the inhibition of brain (Na+ + K+)-ATPase by pyrithiamin.

Brain (Na+ + K+)-ATPase was protected by low concentrations of GSH from the inhibitory effect of pyrithiamin. The possible involvement of sulfhydryl groups in the inhibition was then studied by comparing the effect of pyrithiamin with that of N-ethylmaleimide on the enzyme. The treatment of rat brain (Na+ + K+)-ATPase with thesee inhibitors caused a significant decrease in reactivity of the enzyme to N-ethyl[3H]maleimide. N-Ethylmaleimide, like pyrithiamin, inhibited the partial reactions of (Na+ + K+)-ATPase system in parallel with the inhibition of the overall reaction. An SDS-polyacrylamide gel electrophoresis procedure indicated that pyrithiamin and N-ethylmaleimide inhibited Na+-dependent phosphorylation of the alpha(+) form of rat brain (Na+ + K+)-ATPase more than that of alpha, though the selectivity for the alpha(+) seemed to be higher with the former inhibitor than in the latter. The treatment also decreased sensitivity of the enzyme to ouabain inhibition. However, pyrithiamin- and N-ethylmaleimide-induced inactivations of the enzyme differed in the efficacy of GSH for protection and in the effect of the kind of ligands present during the reaction. Furthermore, pyrithiamin did not appear to interact directly with sulfhydryl groups, but caused the formation of disulfide in bovine brain (Na+ + K+)-ATPase. In contrast to N-ethylmaleimide, pyrithiamin did not affect the sulfhydryl-enzymes such as alcohol dehydrogenase and L-alanine dehydrogenase. It is concluded that pyrithiamin modifies the functional sulfhydryl groups of brain (Na+ + K+)-ATPase in a way different from N-ethylmaleimide and causes a structural change and inactivation of the enzyme.

Animals↗
PubMed1985

Methemoglobinemia diagnosed as a consequence of cardiopulmonary bypass.

Clinically significant methemoglobinemia is rare and difficult to diagnose when other causes of cyanosis are likely. We report a patient in whom unstable angina pectoris and chronic obstructive pulmonary disease were assumed to be responsible for preoperative cyanosis. The use of cardiopulmonary bypass for aortocoronary grafting enabled the clinical diagnosis of methemoglobinemia to be made.

Journal Article↗
PubMed1985

Effects of perinatal Kepone exposure on sexual differentiation of the rat brain.

Timed-pregnant Sprague-Dawley rats were injected intraperitonealy with Kepone dissolved in sesame oil on alternate days beginning on day 18 of gestation and extending through day 7 of lactation with doses of 10 or 5 mg/kg. At 7 days of age the neurologic development of the pups was assessed using the following tests: day of eye opening, occurrence of auditory startle, righting response, reflex suspension, tactile forelimb-placing response, negative geotaxis, and open-field activity. At 70 days of age, vaginal washes from female offspring were examined microscopically for evidence of cyclic activity. At 120 days of age, animals were sacrificed and the brains were examined histologically and the volume of the medial preoptic nucleus was determined. The results indicated that exposure of rat pups to Kepone via either placental and/or milk transfer can result in an acute, or transient, impairment of neurologic development and a possible permanent neuroendocrine impairment. The permanent neuroendocrine dysfunction may be similar to the androgenization phenomenon (i.e., female pups exposed to sex steroids during development) and thus may be related to the reported estrogenic properties of Kepone.

Aging↗
PubMed1984

Stimulation of acetylcholine release from guinea-pig ileal synaptosomes by cyclic nucleotides and forskolin.

Various agents which are known to affect intracellular levels of cAMP have been assessed for their ability to induce the release of [3H]acetylcholine ([3H]ACH) from a synaptosomal preparation derived from the guinea-pig ileum myenteric plexus. 8-Bromo-cAMP increased the release of [3H]ACh above basal levels. While 8-bromo-cGMP also increased the release, this nucleotide was far less potent than 8-bromo-cAMP. Comparison of the release caused by the cyclic nucleotides to the release induced by the nicotinic agonist dimethylphenylpiperazinium (DMPP) suggested that there is some relationship, as yet undefined, between the 8-bromo-cAMP-induced and the DMPP-induced release, while no relationship was evident between the release induced by 8-bromo-cGMP and that caused by DMPP. The 8-bromo-cAMP-induced release was Ca2+-dependent. Neither adenosine, clonidine, nor oxotremorine (all of which modulate the nicotinically-induced release) affected the 8-bromo-cAMP-induced release. The phosphodiesterase inhibitor 3-isobutyl-1-methylxanthine stimulated the release of [3H]ACh as did the adenylate cyclase activator forskolin. The forskolin-induced release was not affected by adenosine, clonidine or oxotremorine. The ability of the modulators to block the nicotinically-induced release but not the release caused by the cyclic nucleotides indicates that the modulation of release evoked by nicotinic activity does not occur at a step involving protein phosphorylation.

1-Methyl-3-isobutylxanthine↗
PubMed1984

The speciation of plutonium in foodstuffs and its influence on gut uptake.

Soluble plutonium complexing agents in foodstuffs have been identified. These have been labelled to high specific activity with 238Pu and their gut uptake determined in rats. The range of values found for naturally-occurring complexes was between 0.03% for oxalate and 0.1% for phytate. However, reasons are advanced for believing that the enhancement of uptake in rats fed the phytate complex would not be expected to occur in man. These results are not taken, therefore, as suggesting that there should be any change in the gut uptake factor of 0.05% currently recommended by the National Radiological Protection Board for plutonium contained in foodstuffs eaten by humans.

6-Phytase↗
PubMed1984

Specific inactivation of alpha (+) molecular form of (Na+ + K+)-ATPase by pyrithiamin.

We have recently reported that pyrithiamin inhibits the activity of (Na+ + K+)-ATPase derived from neuronal but not non-neuronal tissue. In view of the recent demonstration that there are two molecular forms of (Na+ + K+)-ATPase in brain, the present study has examined which form of the enzyme is selectively inhibited by pyrithiamin. Experiments with sodium dodecyl sulfate-polyacrylamide gel electrophoresis showed that the treatment with pyrithiamin decreased the phosphorylation by [gamma-32P]ATP of alpha (+) in a dose-dependent manner while it had little effect on that of alpha. Furthermore, the treatment with pyrithiamin changed the sensitivity of the enzyme to ouabain and N-ethylmaleimide. The specificity of the action of pyrithiamin for alpha (+) was further examined in the developing rat brain (Na+ + K+)-ATPases and peripheral (Na+ + K+)-ATPases from various animals. The molecular form of rat brain (Na+ + K+)-ATPase was primarily alpha on the 14th day of gestation, while it was mainly alpha (+) on the 18th day of gestation and postnatal age. The enzyme from 14-day fetal rat brain was resistant to pyrithiamin inhibition more than other brain enzymes. In cardiac and renal (Na+ + K+)-ATPases from various animals, only the alpha molecular form was found except for dog cardiac preparation which contained alpha (+) and alpha. Pyrithiamin inhibited dog cardiac enzyme activity, while it exerted only minimal inhibition on other peripheral enzymes. It is concluded that pyrithiamin selectively inactivates the alpha (+) molecular form of (Na+ + K+)-ATPase.

Animals↗
PubMed1984

Opiate binding to subcellular fractions from guinea pig ileum.

Binding of 3H-etorphine and 3H-D-Ala2-D-Leu5-enkephalin to opiate receptors in synaptosomal and microsomal fractions prepared from guinea pig ileum homogenates has been studied. It is found that the dissociation constants for etorphine from all fractions are the same. The binding capacity for etorphine for the purified synaptosomal fraction is greater than for other fractions by a factor of 5. For the enkephalin derivative binding to the microsomal fraction the dissociation constant is greater than for etorphine while the binding capacity is a factor of 3 lower. These results are in contrast to the case for binding to central nervous system subcellular fractions.

Animals↗
PubMed1984

Role of synaptosomal Na-accumulation in transmitter release.

The mechanism whereby Na+, K+-ATPase inhibitors such as ouabain trigger transmitter release in a calcium-independent manner remains obscure. We have examined the possible role of intra-synaptosomal sodium ion accumulation in ouabain-induced acetylcholine (ACh) release by: 1) Measuring 22Na accumulation in cat cortical synaptosomes in the presence of ouabain, A23187, veratridine, or strophanthidin over the same time course in which we previously determined their effects on ACh release; and 2) measuring synaptosomal 22Na accumulation and ACh-release in the presence of ouabain plus tetrodotoxin in normal or calcium-free buffer. Our results indicate that tetrodotoxin-dependent 22Na accumulation is at least partially responsible for ouabain-induced ACh release in normal and calcium-free media, but that this ion-accumulation per se is not sufficient to elicit release with other secretogogues.

Acetylcholine↗
PubMed1983

Enzyme system involved in the synthesis of thiamin triphosphate. I. Purification and characterization of protein-bound thiamin diphosphate: ATP phosphoryltransferase.

An enzyme system catalyzing the synthesis of thiamin triphosphate consists of an enzyme (protein-bound thiamin diphosphate:ATP phosphoryltransferase), thiamin diphosphate bound to a macromolecule as substrate, ATP, Mg2+, and a low molecular weight cofactor. This system was established by combining a purified enzyme and an essentially pure, macromolecule-bound substrate prepared from rat livers. This macromolecule was found to be a protein, and the transphosphorylation of thiamin diphosphate to thiamin triphosphate with ATP and enzyme was shown to occur on this macromolecule which binds thiamin diphosphate. Free thiamin, thiamin monophosphate, thiamin diphosphate, and thiamin triphosphate have no effect on this reaction. Thus, the overall reaction is: thiamin diphosphate-protein + ATP in equilibrium thiamin triphosphate-protein + ADP. So-called thiamin diphosphate:ATP phosphoryltransferase (EC 2.7.4.15) activity was not detected in rat brain or liver. The enzyme was extracted from acetone powder of a crude mitochondrial fraction of bovine brain cortex and purified to homogeneity with a 0.6% yield after DEAE-cellulose chromatography, a first gel filtration, hydroxylapatite chromatography, chromatofocusing, and a second gel filtration. The purified enzyme showed a single protein band on polyacrylamide gel electrophoresis in the presence of sodium dodecyl sulfate. Its molecular weight was estimated to be 103,000. The pH optimum was 7.5, and the Km was determined to be 6 X 10(-4) M for ATP. ATP was found to be the most effective phosphate donor among the nucleoside triphosphates. Amino acid analysis of the purified enzyme revealed an abundance of glutaminyl, glutamyl, and aspartyl residues. Sulfhydryl reagents inhibited the enzyme reaction. Metals such as Fe2+, Zn2+, Pb2+, and Cu2+ strongly inhibited the activity. The enzyme was unstable, and glycerol (20%) and dithiothreitol (1.0 mM) were found to preserve the enzyme activity.

Amino Acids↗
PubMed1983

Inhibition of neuronal sodium and potassium ion activated adenosinetriphosphatase by pyrithiamin.

Since one of the electrophysiological effects of pyrithiamin, an antimetabolite of thiamin, suggested an interference with sodium pump mechanisms, the effect of pyrithiamin on Na+,K+-ATPase was investigated. We found that whereas preincubation of the antimetabolite with nonneuronal preparations of Na+,K+-ATPase produced only minimal inhibition, the enzyme derived from brain preparations was markedly inhibited. This inhibition could be prevented by thiamin but not reversed. The kinetic study showed that pyrithiamin acts in a noncompetitive manner with respect to the activation of the enzyme by ATP, Na+, and K+. Pyrithiamin inhibited Na+-dependent phosphorylation and K+-stimulated phosphatase as well as ouabain binding, and these inhibitions were parallel with that of the overall Na+,K+-ATPase reaction. In addition, the antimetabolite caused a significant change in the turbidity of the enzyme suspension. The results suggest that pyrithiamin may induce a structural change of the enzyme complex.

Animals↗
PubMed1983

Cobalt-ions dissociate between calcium uptake through voltage-dependent sodium and calcium channels in synaptosomes.

Calcium ions are taken up through at least two separate, voltage-dependent channels in rat cortical synaptosomes. One channel is opened by 60 mM K+, blocked completely with 500 microM Co2+ and unaffected by 1 microM tetrodotoxin; the other is opened by 20 microM veratridine in a sodium-independent manner, blocked by 1 microM tetrodotoxin, and only partially inhibited by Co2+. Calcium-uptake through either channel is functional with respect to releasing [3H]ACh.

Animals↗