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P-type Ca2+ channels mediate excitatory and inhibitory synaptic transmitter release in crayfish muscle
1Instituto Cajal Consejo Superior de Investigaciones Cientificas, Madrid, Spain.
Abstract:
The toxin fraction (FTX) and peptide omega-Aga-IVA from the venom of the funnel-web spider Agelenopsis aperta, as well as a synthetic analogue of FTX, specifically block the P-type voltage-dependent Ca2+ channel (VDCC). The effects of these toxins on synaptic transmission were studied in the neuromuscular synapses of the crayfish opener muscle, which has a single excitatory and a single inhibitory motoneuron. FTX selectively and reversibly blocked excitatory and inhibitory postsynaptic currents and potentials in a dose-dependent manner. FTX had no effect on (i) resting and postsynaptic membrane conductance, (ii) postsynaptic L-type VDCC, and (iii) both glutamate- and gamma-aminobutyric acid-induced postsynaptic responses. Mean amplitude and frequency of miniature postsynaptic potentials were unchanged by FTX. The postsynaptic VDCC was inhibited by nifedipine, a selective dihydropyridine antagonist of L-type VDCC, whereas synaptic transmission was unaffected. Transmission was also undisturbed by omega-conotoxin, suggesting that N-type VDCCs are not involved. The peptide omega-Aga-IVA blocked excitatory and inhibitory transmission without affecting postsynaptic VDCC. Synaptic transmission was also blocked by synthetic FTX. We conclude that presynaptic P-type VDCCs are involved in both evoked excitatory and inhibitory transmitter release in crayfish neuromuscular synapses.
Insights
Spider venom toxins, specifically P-type voltage-dependent calcium channel (VDCC) blockers, selectively inhibit neurotransmitter release at crayfish neuromuscular synapses. These findings reveal the crucial role of presynaptic P-type VDCCs in synaptic transmission.
Area of Science:
- Neuroscience
- Pharmacology
- Biochemistry
Background:
- Venomous spider toxins are potent modulators of neuronal function.
- Voltage-dependent calcium channels (VDCCs) play critical roles in neurotransmitter release.
- P-type VDCCs are implicated in synaptic transmission, but their specific roles require further elucidation.
Purpose of the Study:
- To investigate the effects of funnel-web spider venom toxins on synaptic transmission.
- To determine the specific type of VDCC involved in neurotransmitter release at crayfish neuromuscular synapses.
- To characterize the action of P-type VDCC blockers on excitatory and inhibitory synaptic currents.
Main Methods:
- Electrophysiological recordings of excitatory and inhibitory postsynaptic currents and potentials in crayfish opener muscle.
- Application of funnel-web spider toxin fraction (FTX), omega-Aga-IVA peptide, and synthetic FTX analogue.
- Pharmacological characterization using nifedipine and omega-conotoxin to probe different VDCC subtypes.
Main Results:
- FTX and omega-Aga-IVA selectively and reversibly blocked excitatory and inhibitory synaptic transmission in a dose-dependent manner.
- These toxins did not affect postsynaptic membrane properties or postsynaptic L-type VDCCs.
- Nifedipine and omega-conotoxin did not inhibit synaptic transmission, indicating L-type and N-type VDCCs are not involved.
Conclusions:
- Presynaptic P-type VDCCs are essential for evoked excitatory and inhibitory neurotransmitter release in crayfish neuromuscular synapses.
- Spider venom toxins targeting P-type VDCCs offer valuable tools for studying synaptic function.
- The findings highlight the specific involvement of P-type VDCCs in regulating transmitter release.