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J G Townsel

Publications and source records attributed to J G Townsel.

At least 19 recordsLinked to original sources
PubMed1995

Cloning and sequencing of a cDNA encoding a novel member of the human brain GABA/noradrenaline neurotransmitter transporter family.

Screening of a human hippocampal cDNA library with a rat creatine transporter cDNA-specific probe revealed two types of clones. One identical to the published creatine transporter cDNA sequence (CRT1) and another (CRT2) with four segments of oligodeoxyribonucleotide substitution or addition in different sites of the CRT1 coding sequence. Translation of the CRT2 coding sequence reveals a new protein with regions of perfect homology with the CRT1 amino-acid sequence.

Amino Acid Sequence↗
PubMed1995

Differential expression and subcellular localization of protein kinase C isoforms in neuronal and cardiac tissues of Limulus polyphemus.

The presence and subcellular distribution of specific protein kinase C (PKC) isoforms in Limulus neuronal and cardiac tissue extracts were determined using polyclonal antibodies to individual PKC isoforms. Western blot analysis revealed that the brain, abdominal ganglia, cardiac ganglia and heart all contained PKC's alpha, beta, gamma, epsilon and zeta. PKC delta was detected in all neuronal tissues. PKC theta was found only in the cardiac ganglia and heart. PKC's gamma and delta were predominantly localized in membrane fractions while the alpha, beta, epsilon, zeta and theta isoforms were found in both fractions. Antibodies to PKC's epsilon and zeta detected relatively high molecular weight bands in membrane fractions and lower molecular weight bands in the cytosolic fractions. The results demonstrate that Limulus neuronal and cardiac tissues differentially express the conventional, novel and atypical isoforms of protein kinase C.

Animals↗
PubMed1995

Neurotransmitter and neuropeptide modulation of high affinity choline uptake in Limulus brain.

The role of neurotransmitters in the modulation of the sodium-dependent high affinity choline uptake system (HAChUS) of the horseshoe crab, Limulus polyphemus has been investigated utilizing a tissue slice preparation. Choline uptake was significantly decreased by carbachol but unaffected by atropine and d-tubocurarine. The muscarinic agonist oxotremorine decreased choline uptake by 30.4% while the muscarinic antagonist, pirenzepine, increased uptake by 29.6%. Applied in combination, pirenzepine and oxotremorine abolished their individual effects resulting in control values for choline uptake. The non-cholinergic transmitters octopamine and serotonin significantly enhanced choline uptake. The neuropeptide proctolin elicited a 20% increase in choline transport whereas Phe-Met-Arg-Phe (FMRF) amide was without effect. This study demonstrates that neurotransmitters and neuropeptides modulate the HAChUS, possibly through specific receptor-mediated second messenger systems.

Animals↗
PubMed1991

An improved invertebrate synaptosomal preparation with cholinergic properties.

Our laboratory has previously characterized a high affinity choline uptake system (HAChUS) in Limulus tissues and synaptosomes. We report here on the characterization of the HAChUS in synaptosomes prepared selectively from central nervous system tissues shown to be enriched for presumed cholinergic functions; namely the protocerebrum, corpora pedunculata and abdominal ganglia. Synaptosomes were prepared from these tissues by means of a modification of the subfractionation procedure developed by Dowdall and Whittaker. In our modification, we harvested a PP2L fraction exclusively from the S2 fraction. Compared to the P2L fraction, the PP2L was greater than three times more efficient in [3H]choline uptake and was significantly more sensitive to inhibition with micromolar concentrations of hemicholinium-3. The PP2L fraction HAChUS was shown to have characteristics common to the HAChUS of identified cholinergic tissues.

Acetylcholine↗
PubMed1989

A vinblastine sensitive high affinity choline uptake system.

1. The Limulus cardiac ganglion high affinity choline uptake system (HAChUS) was inhibited 40, 51 and 64% following pre-exposure to 10, 100 and 500 microM vinblastine, respectively. 2. In contrast, high affinity uptake of choline in the Limulus corpora pedunculata and abdominal ganglia, tissues in which a cholinergic function has been described, were unaffected. 3. In pulse-chase experiments, the cardiac ganglion was incubated in 0.1 microM [3H]choline for 60 min and then switched to an incubation medium containing 1 mM unlabelled choline for varying periods of time. 4. Under these conditions, a 3-fold increase of radiolabel above basal level was measured in the pellet fraction within 2 hr of post-labelling incubation. 5. Prior exposure of the ganglion to 500 microM vinblastine completely eliminated this increase of radioactivity in the pellet fraction. 6. Treatment of the radiolabelled pellet fraction with phospholipase C resulted in the solubilization of 72% of the radiolabel. 7. Ten (10) microM 5-hydroxytryptamine (5-HT), a concentration previously shown to inhibit spontaneous electrical activity within the cardiac ganglion, resulted in a 40% decrease in high affinity choline uptake in this tissue selectively. 8. These results are consistent with the view that a probable role of the Limulus cardiac ganglion HAChUS is the supply of choline subserving the synthesis of membrane phospholipid. 9. It is further speculated that this membrane phospholipid synthesis may be associated with synaptic vesicle turnover.

Animals↗
PubMed1987

The status of the study of invertebrate neurons in tissue culture--phylum Arthropoda.

1. Neurobiological studies employing tissue culture are discussed for all invertebrate organisms in phylum Arthropoda and above. Only arthropod species have been investigated in these studies. 2. The members of phylum Arthropoda utilized were Periplaneta, Locusta, Drosophila, and Schistocerca. 3. Some of the initial studies of nerve cells in tissue culture were performed with Periplaneta and Drosophila; these studies were primarily concerned with differentiation, growth and development. 4. Cultured neurons from cockroach and locust have been used in pharmacological investigations of neurotransmitter receptors. 5. Embryos of the grasshopper Schistocerca were cultured in series of developmental studies related to axon guidance and peripheral nerve formation. 6. Recent studies with Drosophila neurons in vitro have applied a genetic approach to the investigation of molecular properties and function of the axonal sodium channel. 7. An overall view of neuronal tissue culture of invertebrates and analysis of the various areas of research is presented.

Animals↗
PubMed1987

On the status of the study of invertebrate neurons in tissue culture--phyla Mollusca and Annelida.

The utilization of tissue culture in neurobiological studies is discussed for all phyla phylogenetically preceding Phylum Arthropoda. Only two phyla, Mollusca and Annelida, are represented in such studies. The members of Phylum Mollusca which have been so investigated are Aplysia, Helisoma and Lymnaea. The mollusc Aplysia has been used to investigate several processes, including neurosecretion, synaptic transmission and synaptogenesis. Helisoma was employed to study factors regulating neurite growth and the specificity of synapse formation; mechanisms of neurite growth were investigated in the snail Lymnaea. The only member of Phylum Annelida involved in appropriate studies has been the leech Hirudo. This organism was used to investigate axonal regeneration and synaptic mechanisms.

Animals↗
PubMed1987

Biochemical evidence for cholinergic involvement in the Limulus brain.

The transport of [3H]choline by the corpora pedunculata of the circumoesophageal ring gland (brain) of Limulus polyphemus was studied. Corpora pedunculata slices were incubated individually in Chao's solution containing 0.01 microM [3H]choline at room temperature (25 +/- 2 degrees C) and readily accumulated the radiolabel from the extracellular environment. The corpora pedunculata uptake of [3H]choline was linear over 60 min. The kinetic analysis indicated the existence of dual uptake systems for choline within the corpora pedunculata, a high affinity choline uptake process (Km = 0.54 microM and Vmax = 0.037 pmoles/mg/min) and a low affinity process (Km = 137 microM and Vmax = 6.3 pmoles/mg/min). The high affinity choline transport system was dependent on sodium ions and was inhibited by micromolar concentrations of hemicholinium-3. The pre-exposure of the corpora pedunculata to Chao's solution containing 90 mM potassium for 15 min resulted in a 24% increase in the velocity of the high affinity choline uptake process (Vmax = 0.046 pmoles/mg/min). The 90 mM potassium Chao's pretreatment stimulated a substantial increase in the synthesis of [3H]acetylcholine by the corpora pedunculata. The results suggest that the high affinity choline uptake process within the Limulus corpora pedunculata is associated with the synthesis of the transmitter acetylcholine, presumably within cholinergic terminals in this tissue.

Animals↗
PubMed1987

A comparative study of high affinity choline uptake and choline utilization in cholinergic and non-cholinergic tissues.

Comparative studies of [3H]choline accumulation were done in the Limulus corpora pedunculata, abdominal ganglia and cardiac ganglion. Dual uptake processes for choline were found in all three tissues. In acute experiments, the corpora pedunculata high affinity choline uptake system showed exclusive sensitivity to ouabain. Prolonged exposure to ouabain revealed that the HAChUS of all three tissues were significantly inhibited. The metabolism of [3H]choline transported via the high affinity process in the three tissues was studied. [3H]Acetylcholine was a major product of the [3H]choline taken up by the corpora pedunculata and the abdominal ganglia. Phosphorylcholine was the major product seen in cardiac ganglion extracts and occurred in significant proportions in abdominal ganglia extracts. [3H]Acetylcholine was not detected in cardiac ganglion extracts. Treatment with either lithium chloride or hemicholinium-3 markedly inhibited high affinity uptake of [3H]choline in all three tissues.

Animals↗
PubMed1985

The characterization of a sodium-dependent high affinity choline uptake system unassociated with acetylcholine biosynthesis.

The cardiac ganglion of the horseshoe crab, Limulus polyphemus, was incubated in Chao's solution containing 0.01 microM [3H]choline at room temperature (25 +/- 2 degrees C) and the ganglion readily accumulated the radiolabel. The ganglion uptake of [3H]choline was linear over 60 min. Kinetic analysis revealed dual choline uptake systems within the cardiac ganglion, a high affinity uptake system (Km = 2.2 microM, Vmax = 0.16 pmoles/mg/min) and a low affinity system (Km = 92.3 microM, Vmax = 3.08 pmoles/mg/min). The high affinity uptake system was sodium-dependent and inhibited by micromolar concentrations of hemicholinium-3. A 15 min pre-exposure of the ganglion to Chao's solution containing 90 mM potassium stimulated a significant increase in choline uptake. There was no detectable synthesis of [3H]acetylcholine from the [3H]choline taken up by the cardiac ganglion. The major portion of the extractable label appeared in a fraction which co-electrophoresed with phosphorylcholine. These results suggest that the sodium-dependent high affinity [3H]choline uptake system of the cardiac ganglion subserves a specific requirement for choline which is unrelated to a cholinergic function.

Acetylcholine↗
PubMed1982

The use of specific ligands for the vertebrate acetylcholine receptor in the characterization of invertebrate acetylcholine receptors.

1. The interaction of two specific ligands for the vertebrate nicotinic acetylcholine receptor were investigated on the solubilized form of a proposed acetylcholine receptor from the invertebrate Limulus polyphemus. 2. The affinity agent 4-(N-maleimodo)benzyltrimethylammonium iodide exhibited no effect on the binding of alpha-bungarotoxin to the Limulus receptor protein. 3. Torpedo acetylcholine receptor antibody neither inhibited alpha-bungarotoxin binding nor produced any alteration in the sedimentation profile of the Limulus receptor. 4. The lack of interaction of 4-(N-maleimido)benzyltrimethylammonium iodide and Torpedo acetylcholine receptor antibody with the Limulus acetylcholine receptor was interpreted to reflect significant difference between the molecular structures of this invertebrate receptor and the acetylcholine receptor of vertebrate.

Acetylcholine↗
PubMed1981

The effect of alpha-bungarotoxin on spontaneous activity in the ventral nerve cord of Limulus polyphemus.

The physiological action of alpha bungarotoxin in the central nervous system of the horseshoe crab Limulus polyphemus was investigated. Two types of effects were produced by the toxin. The predominant effect was an inhibition of spontaneous activity. However, in some instances alpha bungarotoxin caused a stimulation of activity. In both cases the action of the toxin resembled the effect of d-tubocurarine and opposed the effect of carbamylcholine. Both effects of alpha-bungarotoxin were maximal within 15 min and were sustained for at least 2 h. These results suggest that alpha-bungarotoxin acts as a cholinergic antagonist in the central nervous system of Limulus and are consistent with the specific binding of the toxin to an acetylcholine receptor.

Animals↗
PubMed1980

Alpha-bungarotoxin binding in the central nervous system of Limulus polyphemus.

The binding of 125I-labelled alpha-bungarotoxin in the central nervous system of the horseshoe crab, Limulus polyphemus, was investigated. Comparative binding studies in various tissues of L. polyphemus demonstrated a selective association of the toxin with nervous tissues. The greatest enrichment of toxin binding in subcellular fractions of brain tissue was observed in a fraction enriched in mitochondria and acetylcholinesterase-containing membranes. Autoradiographic studies revealed the localization of alpha-bungarotoxin binding to the longitudinal connectives and neuropile regions of the abdominal ganglia. Three toxin binding components with approximate sedimentation coefficients of 9 S, 15.4 S and 17.4 S were present in solubilized extracts of brain tissue. 125I-labeled alpha-bungarotoxin binding to these components was inhibited 72%, 47%, 9% and 0% by 10 microM concentrations of (+)-tubocurarine, nicotine, scopolamine and pilocarpine, respectively. The apparent formation of the 15.4 S and 17.4 S proteins from the 9 S protein was obtained. The 15.4 S and 17.4 S components are suggested as aggregates of the 9 S protein. This 9 S protein is proposed as an acetylcholine receptor from the central nervous system of L. polyphemus.

Animals↗