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C Hammond

Publications and source records attributed to C Hammond.

At least 19 recordsLinked to original sources
PubMed1992

Characterisation of the L- and N-type calcium channels in differentiated SH-SY5Y neuroblastoma cells: calcium imaging and single channel recording.

We have used single cell imaging of [Ca2+]i and single channel cell-attached patch clamp recording to characterise the Ca2+ channels present on the plasma membrane of retinoic acid-differentiated human neuroblastoma (SH-SY5Y) cells. Exposure to raised K+ (45 or 60 mM) for 1 min resulted in a transient rise in [Ca2+]i which was abolished by cadmium (100 microM). The amplitude of the evoked rise varied from cell to cell. Both omega-Conus toxin (500 nM) and nifedipine (10 microM) reduced, but did not abolish, the rise in [Ca2+]i whereas Bay K 8644 (3 microM) potentiated it. In single channel records both L- and N-type Ca2+ channel openings were observed during membrane depolarisations from a holding potential of -90 mV. L-type channel openings (unitary conductance 22.5 pS) were prolonged by S(+)-PN 202-791 (500 nM) and could still be evoked from a depolarised holding potential (-40 mV). N-type channel openings (unitary conductance 12.5 pS) were unaffected by the dihydropyridine agonist but were inactivated at a holding potential of -40 mV. These results indicate that, in contrast to previous observations using whole cell recording, retinoic acid-differentiated SH-SY5Y cells express both L- and N-type Ca2+ channels.

3-Pyridinecarboxylic acid, 1,4-dihydro-2,6-dimethy↗
PubMed1991

Hirulog peptides with scissile bond replacements resistant to thrombin cleavage.

Using the natural protein hirudin as a model, a novel class of synthetic peptide inhibitors were recently designed. These inhibitors, 'hirulogs', retain the carboxy terminal Hir53-64 domain that interacts with the anion binding exosite of thrombin, connected via an oligoglycyl spacer unit to a catalytic site-directed moiety modeled on the sequence [D]Phe-Pro-Arg-X. The scissile Arg-X bond bond of substrate-like inhibitors has been modified to the proteolytic-resistant functions as beta-homo amino acids Arg psi [CH2CONH] X (2) and reduced bond analogues Arg psi [CH2N]X (3). Both classes of compounds demonstrate inhibition of thrombin amidolytic activity, and this active-site inhibition is highly sensitive to the P1' residue X. Thus these hirulog derivatives are resistant to thrombin proteolysis while maintaining substrate-like interactions with the active center. Finally, hirulog derivatives with non-cleavable replacements of the scissile bond are found to be effective anticoagulant agents.

Amino Acid Sequence↗
PubMed1991

Mu-opioid-receptor-mediated inhibition of the N-type calcium-channel current.

The predominant consequences of mu-opioid-receptor activation are depression of both neuronal activity and transmitter release. Mu-Opioid agonists have previously been observed to increase a potassium conductance and to inhibit adenylate cyclase. We now report that activation of mu-opioid receptors directly decreases the N-type calcium-channel current in a differentiated, human neuroblastoma cell line (SH-SY5Y). The coupling between the mu-opioid receptor and the calcium channel involves a pertussis toxin-sensitive G protein and is independent of changes in adenylate cyclase activity. The inhibition of the calcium-channel current is voltage dependent because it is largely overcome by strong membrane depolarization. It is not associated with changes in the kinetics of current inactivation. Therefore, the mu-receptor belongs to the superfamily of G-protein-coupled, inhibitory neurotransmitter receptors which modulate the activity of calcium and potassium channels and adenylate cyclase.

Adenylate Cyclase Toxin↗
PubMed1990

Efficacy of the metastatic survey in the staging of gestational trophoblastic disease.

Between 1965 and 1987, 190 patients with nonmetastatic and 134 patients with metastatic gestational trophoblastic disease (GTD) underwent initial metastatic survey at the Southeastern Regional Trophoblastic Disease Center (Durham, NC). These patients were evaluated for characteristics which might predict the presence of high-risk metastases before a full radiographic survey was obtained. Minimal staging evaluation of all patients included history and examination, quantitative HCG level by beta-subunit radioimmunoassay, chest radiograph, and evaluation for brain and liver metastases with radionuclide or computed tomography (CT) scans. Seventeen patients had high-risk sites of metastases (i.e., those outside lungs, vagina, or pelvis). Characteristics were identified which might predict high-risk metastases: (1) all had metastases in lungs or vagina; (2) 13 of 17 (76%) had at least one other high risk factor (i.e., beta-HCG titer greater than 40,000 mIU/ml, greater than 4 months since onset of symptoms or antecedent term pregnancy; and (3) 15 of 17 (88%) had obvious symptoms or signs related to high-risk metastasis. The authors then evaluated these criteria to identify high-risk metastasis: (1) asymptomatic patients with GTD are screened for therapy with history and physical examination, HCG level, and chest radiograph or CT of the lungs; and (2) further radiographic imaging is used only for patients with signs or symptoms of high-risk metastases, identifiable lung or pelvic metastases, or other high-risk clinical factors. Using this criteria, patients with high-risk metastases were identified with sensitivity of 100% and specificity of 63%. Approximately 60% of patients did not require further radiographic evaluation.

Angiography↗
PubMed1990

Short related sequences in the cytoplasmic domains of CD4 and CD8 mediate binding to the amino-terminal domain of the p56lck tyrosine protein kinase.

We report that the cytoplasmic domains of the T-lymphocyte glycoproteins CD4 and CD8 alpha contain short related amino acid sequences that are involved in binding the amino-terminal domain of the intracellular tyrosine protein kinase, p56lck. Transfer of as few as six amino acid residues from the cytoplasmic domain of the CD8 alpha protein to the cytoplasmic domain of an unrelated protein conferred p56lck binding to the hybrid protein in HeLa cells. The common sequence motif shared by CD4 and CD8 alpha contains two cysteines, and mutation of either cysteine in the CD4 sequence eliminated binding of p56lck.p56lck also contains two cysteine residues within its CD4-CD8 alpha-binding domain, and both are critical to the interaction with CD4 or CD8 alpha. Because the interaction does not involve disulfide bond formation, a metal ion could stabilize the complex.

Amino Acid Sequence↗
PubMed1989

The lck tyrosine protein kinase interacts with the cytoplasmic tail of the CD4 glycoprotein through its unique amino-terminal domain.

The CD4 lymphocyte surface glycoprotein and the lck tyrosine protein kinase p56lck are found as a complex in T lymphocytes. We have defined the domains in both proteins that are responsible for this interaction by coexpressing hybrid and deleted forms of the two proteins in HeLa cells. We have found that the unique 32 amino-terminal residues of p56lck and the 38 carboxy-terminal residues of CD4 that comprise the cytoplasmic domain are both necessary and sufficient by themselves for the interaction of the two proteins. The interaction appears to be independent of other T cell-specific proteins and probably occurs before CD4 reaches the cell surface. Our findings suggest that the specialized amino-terminal domains of other members of the src family of intracellular tyrosine kinases may also mediate transmembrane signaling via coupling to the cytoplasmic domains of specific transmembrane proteins.

Amino Acid Sequence↗
PubMed1989

Intracellular mechanism of neurotransmitter-induced modulations of voltage-dependent Ca current in snail neurons.

This paper reviews our work on the modulation of voltage-dependent Ca currents in identified snail neurons. Ca currents of snail neurones are enhanced or decreased by neurotransmitters. Serotonin and acetylcholine enhance the Ca current of identified neurons, the effect of serotonin being mediated by cGMP and cGMP-dependent protein kinase. Cholecystokinin (CCK8) and dopamine both decrease the Ca current of identified neurons. The effect of CCK8 is irreversible and involves the activation of protein kinase C. The dopamine-induced decrease in Ca current is reversible and involves an alpha 40 subunit of a snail G protein immunologically and functionally related to alpha o of mammalian brain.

Animals↗
PubMed1988

A method for the assessment of body image disturbance in patients with eating disorders.

This paper describes a new method for assessing body image disturbances in eating disordered patients. Fifteen bulimic, 25 anorexic, and 24 normal controls served as subjects. All subjects were matched for age and height, and bulimics and controls were matched for weight as well. All subjects completed the Perceived Body Image Scale (PBIS), which required subjects to report on how they see themselves when they look in the mirror, how they think they look, and how they feel themselves to be, reflecting the perceptual, cognitive, and affective aspects of body image, respectively. Subjects also selected their ideal. An objective rating was made. Objective ratings had a high correlation with the subject's weight. Results showed that both eating disorder groups demonstrated more apparent body image disturbance than controls, and that the bulimics showed significantly greater body image dissatisfaction than anorexics or controls. The potential use of the PBIS as a research and clinical instrument is discussed.

Adolescent↗
PubMed1988

An alpha 40 subunit of a GTP-binding protein immunologically related to Go mediates a dopamine-induced decrease of Ca2+ current in snail neurons.

Dopamine induces a decrease in voltage-dependent Ca2+ current in identified neurons of the snail H. aspersa. This effect is blocked by intracellular injection of activated B. pertussis toxin and of an affinity-purified antibody against the alpha subunit of bovine Go protein. The dopamine effect is mimicked by intracellular injection of mammalian alpha o. In snail nervous tissue, pertussis toxin ADP-ribosylates a single protein band on SDS gels, and this band is recognized in immunoblots by the anti-alpha o antibody. We propose that this is a 40 kd alpha subunit of a molluscan G protein immunologically related to alpha o and that it mediates the effect of dopamine on Ca2+ currents in identified snail neurons.

Animals↗
PubMed1986

Stimulation of the subthalamic nucleus enhances the release of dopamine in the rat substantia nigra.

The release of dopamine in the substantia nigra and striatum was investigated in halothane anaesthetized rats by means of the push-pull cannula method. Electrical stimulation of the subthalamic nucleus produced a marked enhancement of dopamine release in the ipsilateral substantia nigra. This effect is likely to be mediated by subthalamic efferent neurons since the application of acetylcholine in the subthalamic nucleus produced a similar effect. A later decrease of dopamine release was always observed in the ipsilateral striatum and was attributed to the autoregulation mechanisms of nigro-striatal dopaminergic neurons.

Animals↗
PubMed1986

Excitatory effect of iontophoretically applied dopamine on identified neurons of the rat subthalamic nucleus.

The effects of iontophoretic applications of dopamine were studied on neurons of the subthalamic nucleus (STN) identified by their histological location, their response to contralateral vibrissae stimulation and, for 33% of them, by their antidromic activation from the globus pallidus. A potent and consistent excitatory effect of dopamine was found for all the STN neurons tested. Depression of spontaneous activity or mixed responses were never recorded in the STN. The excitatory response was antagonized by iontophoretic application of flupenthixol.

Animals↗
PubMed1986

Serotonin and cyclic GMP both induce an increase of the calcium current in the same identified molluscan neurons.

Serotonin (5-HT) has previously been shown to evoke an increase in the duration of the Ca2+-dependent spike of molluscan neurons by decreasing the S current (Klein et al., 1982), a K+ current controlled by cAMP. However, in a group of identified ventral neurons of the snail Helix aspersa in which 5-HT (1-10 microM) also prolonged the duration of the Ca2+-dependent action potential, no 5-HT-induced depression of S current or of any other outward current was observed. Instead, 5-HT was found to evoke the prolongation of the somatic spike by inducing an increase in Ca2+ membrane conductance. This 5-HT-induced increase of Ca2+-current was mimicked neither by the intracellular injection of cAMP nor by the extracellular application of forskolin (20 microM). In contrast, it was mimicked by the intracellular injection of cGMP and by the extracellular application of 100 nM zaprinast, a cGMP-phosphodiesterase inhibitor. The extracellular application of phorbol ester TPA (100 nM), an activator of protein kinase C, was also found to increase the Ca2+ current in the identified snail ventral neurons, but this enhancing effect had a different time course from that induced by 5-HT. These results indicate that there is a second mechanism for prolonging the Ca2+ spike of molluscan neurons, consisting of an increase in Ca2+ current, in which cGMP may play a role as second messenger.

Action Potentials↗
PubMed1985

Nucleotide sequence and topography of chicken c-fps. Genesis of a retroviral oncogene encoding a tyrosine-specific protein kinase.

We isolated molecular clones of chicken DNA that carry portions of the cellular proto-oncogene c-fps and then determined the nucleotide sequence of all regions of the gene that are related to the retroviral oncogene v-fps. The homology of v-fps within c-fps resides on at least 19 interspersed segments, 17 of which represent complete exons and two of which may represent only portions of exons. Fusion of these segments reconstructs a facsimile of v-fps. The arrangement of introns and exons within c-fps differs from that of the related proto-oncogene c-src in the domains of the two genes that encode tyrosine-specific protein kinase activity. It therefore appears likely that the introns arose subsequent to the gene duplication that engendered c-src and c-fps. The data also reveal potential junctions between viral and cellular domains in the genomes of two independently isolated avian sarcoma viruses (the PRCII and Fujinami strains). The lefthand junctions can be well defined: they occur at the same position in c-fps but at different positions in the viral gene gag. The righthand junctions cannot be defined as precisely because they include a sequence of 10 to 15 nucleotides whose origin is not known. In the genome of PRCII virus, the composition of this sequence suggests that it arose from the polyadenylated 3' terminus of the c-fps messenger RNA. If this deduction proves to be correct, the data will provide direct evidence that the righthand recombination during transduction by retroviruses occurs between RNA intermediates. Irrespective of these ambiguities, both junctions are located within exons of c-fps, and both may have been formed by non-homologous recombination (although the evidence for the latter statement is not decisive). A sequence of 1020 nucleotides has been deleted from the transduced version of c-fps in the genome of PRCII virus, apparently by homologous recombination between sequences repeated within c-fps. Fujinami virus may contain the entire coding domain of c-fps, but mutations have created 26 amino acid substitutions in the viral version of the gene. By contrast, the partially deleted version of c-fps in PRCII virus contains no mutations that would alter the amino acid sequence.

Amino Acid Sequence↗
PubMed1983

Microiontophoretic studies on the nature of the neurotransmitter in the subthalamo-entopeduncular pathway of the rat.

The aim of the present study was to determine the identity of the neurotransmitter released by the pathway from the subthalamic nucleus to the entopeduncular nucleus in the rat, using extracellular stimulating and recording techniques and microiontophoresis. In order to avoid stimulation of passing fibers at the level of the subthalamic nucleus, (collaterals to the entopeduncular nucleus of the caudato-nigral pathway, or direct projections to the entopeduncular nucleus from the substantia nigra or nucleus tegmenti pedunculopontinus), the experiments were performed in rats bearing chronic ipsilateral lesions in order to make these pathways degenerate. Under such conditions, subthalamic nucleus stimulation suppressed the spontaneous firing of all the entopeduncular nucleus cells studied (n = 40) for 15-25 ms (mean duration +/- S.E.M.:21.88 +/- 1.57 ms). Entopeduncular nucleus cells were identified by antidromic activation from the ventral anterior thalamic nucleus (40%) or lateral habenula nucleus (68%). Low doses of iontophoretically applied GABA (60 cells) or glycine (15 cells) were inhibitory upon entopeduncular cells, while acetylcholine or carbamylcholine were poorly excitatory (18 cells), or had no effect (28 cells). The subthalamic nucleus-evoked inhibition of entopeduncular neurons was reversed by microiontophoretically applied bicuculline or picrotoxin, at doses which blocked the GABA-induced response, but not that produced by glycine or acetylcholine. With similar experiments, strychnine and atropine were ineffective. This excludes a possible role of glycine or acetylcholine in the subthalamic-evoked inhibitory response of entopeduncular cells. The present study strongly suggest that GABA is a neurotransmitter in the inhibitory subthalamo-entopeduncular pathway.

Acetylcholine↗
PubMed1979

Pharmacological properties of acetylcholine-induced excitation of subthalamic nucleus neurones.

1. In 15 rats anaesthetized with ketamine, microiontophoretically applied acetylcholine (ACh) excited all 58 cells studied in the subthalamic nucleus (STN). 2. The ACh-evoked excitation was slow in onset and outlasted the ACh application. There was no sign of desensitization when the ACh application was prolonged or repeated. The excitation was prolonged by a concomitant application of physostigmine. 3. Acetyl-beta-methyl choline and oxotremorine were effective cholinomimetics. Nicotine had no effect. 4. The ACh excitation was antagonized by stropine and scopolamine but not by mecamylamine. 5. It was condluded that STN ACh receptors are muscarinic in character. 6. Since large microiontophoretic applications of Mg2+ did not suppress ACh-evoked excitation, it is suggested that ACh acts postsynaptically. 7. The excitatory response of STN cells to striatal or pallidal stimulation was unaffected by atropine administered either microiontophoretically to single cells or intravenously (3 mg/kg) to the whole animal.

Acetylcholine↗