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Differential sensitivity of synaptosomal calcium entry and endogenous dopamine release to omega-conotoxin
J J Woodward1, S M Rezazadeh, S W Leslie
1Division of Pharmacology, College of Pharmacy, University of Texas, Austin 78712.
Abstract:
The presynaptic neurotoxin omega-conotoxin (omega-CgTx) was tested for its ability to inhibit voltage-dependent calcium flux and transmitter release in rat brain synaptosomes. Conotoxin (0.001-10 microM) had no effect on calcium uptake or endogenous dopamine release from rat striatal synaptosomes in the absence of potassium depolarization. Fast-phase potassium stimulated calcium influx was only partially (20-30%) inhibited by conotoxin at concentrations between 1 nM and 10 microM. The fast-phase release of endogenous dopamine from the same synaptosomal preparation was inhibited by approximately 25% at 0.01 microM and by 60% at 10 microM. These results suggest that a subgroup of high affinity omega-CgTx-sensitive calcium channels may be involved in regulating the release of endogenous dopamine from brain synaptosomes.
Insights
Omega-conotoxin (omega-CgTx) partially inhibits calcium influx and dopamine release in rat brain synaptosomes. These findings suggest specific omega-CgTx-sensitive calcium channels regulate dopamine release.
Area of Science:
- Neuroscience
- Neuropharmacology
Background:
- Presynaptic neurotoxins like omega-conotoxin (omega-CgTx) are crucial tools for studying neuronal function.
- Voltage-dependent calcium channels play a key role in neurotransmitter release.
Purpose of the Study:
- To investigate the effects of omega-conotoxin on calcium influx and dopamine release in rat brain synaptosomes.
- To determine the affinity and sensitivity of calcium channels involved in dopamine release.
Main Methods:
- Rat striatal synaptosomes were used to measure calcium uptake and endogenous dopamine release.
- The effects of varying concentrations of omega-conotoxin were assessed in the presence and absence of potassium depolarization.
Main Results:
- Omega-conotoxin did not affect basal calcium uptake or dopamine release.
- Potassium-stimulated calcium influx was partially inhibited (20-30%) by omega-conotoxin.
- Dopamine release was inhibited by approximately 25% at 0.01 microM and 60% at 10 microM omega-conotoxin.
Conclusions:
- A subset of high-affinity omega-conotoxin-sensitive calcium channels likely regulates endogenous dopamine release from brain synaptosomes.
- These findings contribute to understanding the specific calcium channel subtypes involved in dopaminergic neurotransmission.