Biomedical subjects

M T Ivy

Publications and source records attributed to M T Ivy.

6 recordsLinked to original sources

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↗

PubMed1988

Evidence to suggest that the spontaneous release of acetylcholine from rat hippocampal tissue is carrier-mediated.

The effect of L- and D-stereoisomers of 2-(4-phenylpiperidino) cyclohexanol (AH 5183) on the spontaneous release of acetylcholine (ACh) from rat hippocampal tissue was studied. L-AH 5183 was approximately 100 times more potent than was D-AH 5183 in reducing spontaneous ACh release. Spontaneous ACh release was also temperature dependent. These results may suggest that the spontaneous release of ACh from brain tissue is carrier-mediated.

Acetylcholine↗

PubMed1988

Effect of 2-(4-phenylpiperidino)cyclohexanol (AH 5183) on the veratridine-induced increase in acetylcholine synthesis by rat hippocampal tissue.

The intent of this study was to determine whether the drug 2-(4-phenylpiperidino)cyclohexanol (AH 5183 or vesamicol) might inhibit the veratridine-induced increase in acetylcholine (ACh) synthesis by reducing the veratridine-induced activation of a detergent-soluble choline-O-acetyltransferase (EC 2.3.1.6; ChAT) fraction associated with a vesicle-bound store of ACh. When minces of rat hippocampal tissue were loaded with [14C]choline and subsequently depolarized with veratridine, an increase in the synthesis of [14C]ACh occurred that could be abolished by L-AH 5183 (75 nM). When minces were depolarized with veratridine in the presence of L-AH 5183 (75 nM), the depolarization-induced activation of a detergent-soluble ChAT fraction associated with a vesicle-bound store of ACh was blocked. Conversely, the veratridine-induced activation of a water-soluble ChAT fraction believed to be cytosolic was not. AH 5183 also blocked the repletion of the vesicle-bound store with newly synthesized ACh following veratridine-induced depletion of ACh, a result that appeared to be mediated by an effect on the synthesis of ACh at the vesicular surface. These results suggest that veratridine depolarization of rat hippocampal nerve terminals stimulates the synthesis of ACh by activating a detergent-soluble fraction of ChAT closely associated with synaptic vesicle release sites. ACh synthesis and transport at the vesicular surface may be influenced by a common AH 5183-sensitive regulatory protein.

Acetylcholine↗

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↗