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Biomedical subjects

E Cooper

Publications and source records attributed to E Cooper.

At least 91 records · Page 5Linked to original sources
PubMed1989

Interrelationship between cortisol and atrial natriuretic factor in the immature ovine fetus.

1. In chronically cannulated ovine fetuses (100-130 days of gestation) the infusion of cortisol (86.7 +/- 15 micrograms/h for 4 h) or human atrial natriuretic factor (ANF; 4.4 micrograms for 2 h) resulted in highly significant increases in the excretion of sodium, chloride, potassium and water. 2. Cortisol had no significant effect on fetal plasma ANF concentrations. All values are mean and s.e.m. Plasma immunoreactive ANF was 53 +/- 5 and 67.3 +/- 13 pmol/L in the 4 h saline infused fetuses, and 51.3 +/- 14.3 and 74 +/- 13.3 pmol/L in cortisol-infused fetuses (n = 7). A separate group of fetuses received 2 h infusions of saline or hANF (4.4 micrograms/h), and plasma IR-ANF values were measured (n = 3). The values, at 0, 60, 90 and 120 min were, respectively, 19.7 +/- 3, 17.3 +/- 0.7, 18.7 +/- 3.7 and 20.7 +/- 3.7 pmol/L in the saline infused group, and 25.3 +/- 5.3, 80.7 +/- 32.3, 123.3 +/- 4.3 and 100 +/- 15 pmol/L in the ANF-infused fetuses. 3. Blood cortisol concentrations, in fetuses infused for 4 h with 0.9% NaCl, were 3.1 +/- 0.8 nmol/L (n = 7); in fetuses infused with 0.9% NaCl for 2 h were 3.6 +/- 1 nmol/L (n = 3); in fetuses infused for 4 h with cortisol were 19.9 +/- 1.9 nmol/L (n = 7); and in fetuses infused with hANF for 2 h were 6.0 +/- 3.0 nmol/L (n = 5). 4. There was no effect of fetal hANF infusion on maternal or fetal blood aldosterone concentrations.(ABSTRACT TRUNCATED AT 250 WORDS)

Aldosterone↗
PubMed1988

Electrophysiology of a chick neuronal nicotinic acetylcholine receptor expressed in Xenopus oocytes after cDNA injection.

Brain nicotinic acetylcholine receptors (nAChRs) are made up of protein subunits that differ from those constituting muscle nAChRs. To characterize the physiological properties of one class of avian brain nicotinic receptor, we injected the nuclei of Xenopus oocytes with full-length cDNAs for the ligand binding (alpha 4) and structural (n alpha) subunits. Injected oocytes had large ACh-induced currents in the microampere range that were insensitive to alpha-bungarotoxin, as expected for neuronal nAChRs. We found that these brain nAChRs incorporate at least two alpha 4 subunits and that their functional properties differ from muscle nAChRs in at least two respects: the elementary conductance is considerably smaller (20 pS), and channels in outside out patches stop functioning within a few minutes.

Animals↗
PubMed1988

Membrane currents of rat satellite cells attached to intact skeletal muscle fibers.

Muscle satellite cells play an important role in the postnatal growth of skeletal muscle and in the regeneration of damaged muscle during adult life. Little is known about the physiological properties of satellite cells in their dormant state as they lie adjacent to the intact muscle fibers, underneath the basement membrane. Our recent experiments, using patch clamp techniques, indicate that no tight electrical coupling is present between satellite cells and the muscle fiber dissociated from rat flexor digitorum brevis. Satellite cells possess sodium channels with low sensitivity to tetrodotoxin and at a much lower density than muscle. In addition, satellite cells are insensitive to acetylcholine (ACh) for at least 24 hr after having been removed from the animal, even when detached from their muscle fiber. However, we could measure ACh-evoked currents from satellite cells 48-72 hr in culture, indicating that ACh sensitivity develops with time.

Acetylcholine↗
PubMed1987

Rapid and selective effects of thyrotropin on [35S]methionine incorporation into cytoplasmic and nuclear proteins in calf thyroid tissue slices.

Previous studies have indicated that thyrotropin may induce general increases in RNA and protein synthesis in calf thyroid tissue slices. In this report, we show that thyrotropin selectively stimulates [35S]methionine incorporation into small numbers of specific cytoplasmic and nuclear proteins. We provide data on the time course of stimulation and on relative molecular masses and isoelectric points of hormone-response proteins. Calf thyroid tissue slices were incubated for 3 h, 6 h or 9 h in the presence or absence of thyrotropin (50 mU/ml); [35S]methionine (50-75 microCi/ml) was added for the final 3 h of incubation. Cytoplasmic and nuclear fractions were then prepared, and analyzed by two-dimensional polyacrylamide gel electrophoresis and fluorography. Thyrotropin increased [35S]methionine incorporation into two cytoplasmic and four nuclear proteins within 3 h; hormonal effects on the labeling of five of these six proteins were transient, and no longer evident after 6-9 h. In contrast, a second group of two cytoplasmic and four nuclear proteins exhibited increased labeling after a delay of 6-9 h. Our results suggest that thyrotropin selectively stimulates the synthesis of specific cytoplasmic and nuclear proteins in calf thyroid tissue slices, and that stimulation involves at least two mechanisms (one rapid, the other delayed).

Animals↗
PubMed1986

Factors affecting the expression of acetylcholine receptors on rat sensory neurones in culture.

Sensory neurones from nodose ganglia of new-born rats were grown in dissociated tissue culture either with or without satellite cells. When cultured without satellite cells, most neurones developed sensitivity to acetylcholine (ACh); time-course experiments indicated that the neurones acquire their sensitivity during the second to third week in culture. Most neurones co-cultured with satellite cells did not develop ACh sensitivity. Delayed removal of satellite cells 8-12 days after plating resulted in few neurones acquiring ACh sensitivity. Delayed addition of satellite cells to neuronal cultures that were initially grown without satellite cells had no effect on the number of ACh-sensitive neurones. The potential to develop ACh sensitivity in culture without satellite cells decreases with the age of the neurones at the time of culturing; few neurones from 2-week-old animals developed sensitivity to ACh when cultured without satellite cells. These results indicate that there is some influence from satellite cells that prevents nodose neurones from developing ACh sensitivity in culture and suggests that this influence may also operate in vivo.

Acetylcholine↗
PubMed1985

Hormonal control of the phosphorylation of histones, HMG proteins and other nuclear proteins.

Hormone-dependent phosphorylation and dephosphorylation of nuclear proteins may play an important part in regulating nuclear function and specific gene expression. Some progress has been made in identifying specific nuclear proteins whose phosphorylation is affected by specific hormones; however, relatively little is known about the regulatory mechanisms involved, or about the molecular consequences of increased or decreased phosphorylation. It is suspected--but not yet proved--that cAMP-dependent effects on transcription are mediated at least partly by increases in nuclear cAMP-dependent protein kinase (A-kinase) activity, and consequent increases in the phosphorylation of specific chromatin proteins. In several instances, increased phosphorylation has been found to precede or correlate with cAMP-mediated induction of specific gene products. Several chromatin proteins are susceptible to cAMP-dependent phosphorylation in vivo, including histones H1 and H3, the high mobility group protein HMG 14 (which is preferentially associated with actively transcribed chromatin), and at least three other basic nonhistone proteins. The A-kinase phosphorylation sites of the majority of H1, H3 and HMG 14 molecules in chromatin appear to be inaccessible to A-kinase in vivo; nothing is known about the factors determining their accessibility, which may be tightly regulated and may vary significantly from cell to cell and tissue to tissue. Many hormone-induced changes in nuclear protein phosphorylation may be cAMP-independent. cAMP-independent mechanisms could involve a variety of nuclear enzymes including, for example, cGMP-dependent, Ca2+/calmodulin-dependent, Ca2+/phospholipid-dependent and polyamine-dependent protein kinases. So far, however, there is little solid evidence in support of a role for any specific cAMP-independent protein kinase in mediating hormonally induced increases in the phosphorylation of specific, identified nuclear proteins.

Animals↗
PubMed1985

Single-channel analysis of fast transient potassium currents from rat nodose neurones.

Single channels that underlie the fast transient potassium current (IA) were recorded, using patch-clamp techniques, from cultured sensory neurones. The open channel conductance was approximately 22 pS, and was constant over most of the physiological voltage range; single-channel conductance decreased at more depolarized levels. Summing single-channel currents resulted in an average current whose kinetics were similar to the macroscopic IA. The inactivation of these currents, at the potentials we studied, was fitted with a single exponential with a time constant of approximately 30 ms. For the currents evoked by large depolarizing steps (to +40 mV), the mean channel open time equals approximately 30 ms. For currents evoked at less depolarized levels (to 0 mV), the mean open time equals approximately 15 ms, half the inactivation time constant.

Action Potentials↗
PubMed1985

Thymic seminoma and myasthenia gravis.

Computed tomography detected an enlarged thymus in a 27-year-old man with myasthenia gravis of recent onset. Pathological examination of the thymus revealed lymphoid hyperplasia and a thymic seminoma (or germinoma), which was arising as an intramural nodule in a thymic cyst. This is the first reported association of thymic seminoma, lymphoid hyperplasia, and myasthenia gravis.

Adult↗
PubMed1984

Thyrotropin-stimulated phosphorylation of high mobility group protein 14 in vivo at the site catalyzed by cyclic nucleotide-dependent protein kinases in vitro.

Thyrotropin (TSH) treatment of bovine thyroid slices increased 32P-labeling of chromosomal high mobility group 14 (HMG) protein approximately 2-fold. Analogs of cAMP, but not cGMP, also enhanced phosphorylation of HMG 14. The sites of phosphorylation were analyzed by partial acid hydrolysis and by two-dimensional mapping of tryptic digests of 32P-labeled HMG 14 which was purified from control and TSH-treated thyroid tissue. TSH treatment enhanced phosphorylation at serine residues in four prominent tryptic phosphopeptides which were identical with those derived from HMG 14 phosphorylated in vitro with cAMP- and cGMP-dependent protein kinases. The four tryptic phosphopeptides contain serine 6, the major site of in vitro phosphorylation catalyzed by cyclic nucleotide-dependent protein kinases (Walton, G. M., Spiess, J., and Gill, G. N. (1982) J. Biol. Chem. 257, 4661-4668). TSH did not affect phosphorylation of serine 24, a minor site of phosphorylation in vitro. These studies suggest that TSH-stimulated phosphorylation of HMG 14 is catalyzed by cAMP-dependent protein kinase.

Amino Acids↗
PubMed1984

Synapse formation among developing sensory neurones from rat nodose ganglia grown in tissue culture.

Sensory neurones from new-born rat nodose ganglia were grown in tissue culture, either with or without the ganglionic satellite cells, in order to investigate influences of satellite cells on sensory neurone development. To learn more about the post-natal development of nodose ganglia in rats neuronal counts of the ganglion were made at three different developmental stages. There were no significant differences of neuronal number in nodose ganglia in new-born rats, rats 3 weeks of age, and adult rats. Up to 60% of the neurones formed synapses with each other when they developed in culture without ganglion satellite cells. Pharmacological experiments indicated that the transmitter at these synapses was ACh and the post-synaptic receptors were nicotinic. Neurones co-cultured with satellite cells rarely formed functional synapses and most (85%) were not sensitive to ACh: 75% of neurones cultured without satellite cells were ACh sensitive. These results provide evidence that mammalian sensory neurones form synapses among each other in culture. The results also suggest that ganglionic satellite cells prevent functional synapses among these neurones from occurring, in part because the neurones do not express ACh sensitivity when co-cultured with satellite cells.

Acetylcholine↗
PubMed1984

Effects of cycloheximide, alpha-amanitin, and alpha-difluoromethylornithine on thyrotropin-induced increases in the micrococcal nuclease sensitivity of thyroid nuclear chromatin.

Treatment of calf thyroid slices with TSH increases the nuclease sensitivity of nuclear chromatin, i.e. the amount of DNA released from nuclei by mild digestion with DNase I and micrococcal nuclease. Cycloheximide and alpha-amanitin were used to investigate the roles played by protein and RNA synthesis in mediating this effect of TSH; alpha-difluoromethylornithine, an irreversible inhibitor of ornithine decarboxylase, was used to investigate the possible involvement of polyamines. Calf thyroid slices were incubated with or without TSH (50 mU/ml) for 5 h, in the presence or absence of inhibitors. Nuclei were then prepared, subjected to mild digestion with micrococcal nuclease, and centrifuged at 1200 X g. The amount of DNA in 1200 X g supernatants was increased by TSH; this was inhibited by cycloheximide (100 micrograms/ml) and alpha-amanitin (4 micrograms/ml) when these agents were present throughout incubations with TSH. In contrast, alpha-amanitin failed to inhibit the TSH effect when it was added to incubations 30 min or 2 h after the addition of TSH. These results indicate that RNA and protein synthesis play a part in mediating the effect of TSH on the micrococcal nuclease sensitivity of chromatin, and that the RNA synthesis involved takes place within the first 30 min of exposure of thyroid slices to TSH. alpha-Difluoromethylornithine (5 mM) inhibited the TSH-dependent development of micrococcal nuclease sensitivity; however, it also inhibited nuclease digestion when it was added directly to nuclei prepared from fresh thyroid tissue. This observation should serve as a warning against uncritical acceptance of the notion that all effects of alpha-difluoromethylornithine are the result of inhibition of ornithine decarboxylase.

Amanitins↗
PubMed1984

Histone and high mobility group protein phosphorylation in the thyroid: regulation by cyclic nucleotides.

A variety of cyclic nucleotide analogs and other agents that affect thyroid cyclic nucleotide metabolism were used to investigate the role of cAMP and cGMP in regulating nuclear protein phosphorylation in calf thyroid slices labeled in vitro with [32P]orthophosphate. Two major groups of acid-soluble proteins were studied. Group I consisted of proteins whose phosphorylation is stimulated by TSH [histones H1 and H3, high mobility group (HMG) protein 14, and the HMG 14/17-like protein PS.3]; group II included representatives of a spectrum of proteins whose phosphorylation is unaffected by TSH (histones H2A, H2B, and H4, HMG 17, the HMG 14/17-like protein PS.2, and the nonhistone protein AS.1). The effects of TSH (50 mU/ml) on the 32P labeling of group I proteins were partially reproduced by (Bu)2cAMP (1 mM), 8-bromo-cAMP (1 mM), and butyrate (2 mM), and closely mimicked by 8-(4-chlorophenylthio)cAMP (1 mM), forskolin (25 microM), and butyrate (10 mM). (Bu)2cGMP (1 mM), 8-bromo-cGMP (1 mM), and carbachol (50 microM) had no effect on protein phosphorylation. NaNO2 (20 mM), which markedly increases cGMP concentration in calf thyroid slices, decreased the 32P labeling of group I proteins and also affected, to varying extents, the phosphorylation of the group II proteins. The phosphodiesterase inhibitor methylisobutylxanthine (0.5 mM) had generally minor effects on 32P labeling; however, it did counteract the effects of NaNO2 on group I protein phosphorylation. Our results provide strong support for the hypothesis that TSH-dependent phosphorylation of group I proteins is mediated by cAMP, but they provide little evidence of cGMP regulation of histone or HMG protein phosphorylation.

1-Methyl-3-isobutylxanthine↗
PubMed1984

Familial nasopharyngeal carcinoma.

We report 3 cases of nasopharyngeal carcinoma occurring in a single family group. All 3 patients are male, caucasian, born in Australia and of Greek origin. Two of the patients are brothers, the third their first cousin.

Adult↗
PubMed1984

Growth faltering lacks association with the distribution of first year deaths.

A retrospective study of infant mortality from death registers was made in St Lucia and St Vincent. In both islands postneonatal deaths by month were found to be evenly distributed throughout the first year although the total infant mortality rates differed widely. The growth of a cohort of children from three St Lucian villages was studied. Their weight curve showed 'faltering' at 3 months, closely resembling the developing world pattern described by Waterlow, Ashworth & Griffiths (1980). We therefore conclude that there is no necessary association between this pattern of infant growth and infant mortality rate, nor between the distribution of weight velocity and the distribution of deaths in the first year.

Birth Certificates↗