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Neurotransmitter release from tottering mice nerve terminals with reduced expression of mutated P- and Q-type
A G Miriam Leenders1, Arn M J M van den Maagdenberg, Fernando H Lopes da Silva
1Swammerdam Institute for Life Sciences, Section Neurobiology, Faculty of Science, University of Amsterdam, Kruislaan 320, 1090 GB Amsterdam, The Netherlands.
Abstract:
Neurotransmitter release is triggered by Ca2+-influx through multiple sub-types of high voltage-activated Ca2+-channels. Tottering mice have a mutation in the alpha1A pore-forming subunit of P- and Q-type Ca2+-channels, two prominent sub-types that regulate transmitter release from central nerve terminals. Immunoblotting analysis of purified forebrain terminals from tottering mice revealed an 85% reduction in the protein expression level of the mutated alpha1A subunit compared to expression of the alpha1A subunit in wild-type terminals. In contrast, the expression of the alpha1B subunit of the N-type Ca2+-channels was unchanged. Release of the amino acids glutamate and GABA and of the neuropeptide cholecystokinin (CCK) induced by a short (100 ms) depolarization pulse was unchanged in the terminals of tottering mice. Studies using specific blockers of Ca2+-channels however, revealed a reduced contribution of P- and Q-type Ca2+-channels to glutamate and cholecystokinin release, whereas a greater reliance on N-type Ca2+-channels for release of these transmitters was observed. In contrast, the contribution of the P-, Q- and N-type Ca2+-channels to the release of GABA was not altered in tottering mice. These results indicate that the expression of the alpha1A subunit was decreased in terminals from tottering mice, and that a decreased contribution of P- and Q-type Ca2+-channels to the release of glutamate and cholecystokinin was functionally compensated by an increased contribution of N-type Ca2+-channels.
Insights
Tottering mice show reduced alpha1A calcium channel subunits, impacting neurotransmitter release. Compensatory mechanisms increase N-type channel reliance for glutamate and CCK release, maintaining GABA release.
Area of Science:
- Neuroscience
- Molecular Biology
- Neuropharmacology
Background:
- Neurotransmitter release relies on calcium (Ca2+) influx via high voltage-activated Ca2+-channels.
- Tottering mice possess a mutation in the alpha1A subunit of P/Q-type Ca2+-channels, crucial for central nerve terminal function.
Purpose of the Study:
- To investigate the impact of the alpha1A subunit mutation in tottering mice on neurotransmitter release mechanisms.
- To determine if altered P/Q-type Ca2+-channel function is compensated by other Ca2+-channel subtypes.
Main Methods:
- Immunoblotting to quantify alpha1A and alpha1B Ca2+-channel subunit expression in tottering and wild-type mouse forebrain terminals.
- Measurement of glutamate, GABA, and cholecystokinin (CCK) release upon depolarization.
- Utilizing specific Ca2+-channel blockers to assess the contribution of different channel subtypes to neurotransmitter release.
Main Results:
- Tottering mice exhibited an 85% reduction in alpha1A subunit protein expression, with unchanged alpha1B subunit levels.
- Glutamate and CCK release were not altered overall but showed reduced dependence on P/Q-type channels and increased reliance on N-type channels.
- GABA release remained unaffected by the mutation across P-, Q-, and N-type Ca2+-channels.
Conclusions:
- The alpha1A subunit mutation in tottering mice leads to decreased P/Q-type Ca2+-channel contribution to glutamate and CCK release.
- Functional compensation occurs via increased N-type Ca2+-channel activity for these transmitters.
- GABA release mechanisms are not significantly impacted by the altered P/Q-type Ca2+-channel function.