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P-type voltage-dependent calcium channel mediates presynaptic calcium influx and transmitter release in mammalian
O D Uchitel1, D A Protti, V Sanchez
1Instituto de Biologia Celular Facultad de Medicina, Universidad de Buenos Aires, Argentina.
Abstract:
We have studied the effect of the purified toxin from the funnel-web spider venom (FTX) and its synthetic analog (sFTX) on transmitter release and presynaptic currents at the mouse neuromuscular junction. FTX specifically blocks the omega-conotoxin- and dihydropyridine-insensitive P-type voltage-dependent Ca2+ channel (VDCC) in cerebellar Purkinje cells. Mammalian neuromuscular transmission, which is insensitive to N- or L-type Ca2+ channel blockers, was effectively abolished by FTX and sFTX. These substances blocked the muscle contraction and the neurotransmitter release evoked by nerve stimulation. Moreover, presynaptic Ca2+ currents recorded extracellularly from the interior of the perineural sheaths of nerves innervating the mouse levator auris muscle were specifically blocked by both natural toxin and synthetic analogue. In a parallel set of experiments, K(+)-induced Ca45 uptake by brain synaptosomes was also shown to be blocked or greatly diminished by FTX and sFTX. These results indicate that the predominant VDCC in the motor nerve terminals, and possibly in a significant percentage of brain synapses, is the P-type channel.
Insights
Funnel-web spider toxin (FTX) and its analog block P-type calcium channels, crucial for neurotransmitter release at neuromuscular junctions and brain synapses. This finding impacts understanding of synaptic transmission.
Area of Science:
- Neuroscience
- Pharmacology
- Molecular Biology
Background:
- Voltage-dependent calcium channels (VDCCs) are critical for neurotransmitter release.
- Different VDCC subtypes (N, L, P) mediate distinct physiological functions.
- The role of specific VDCC subtypes in mammalian neuromuscular transmission requires further elucidation.
Purpose of the Study:
- To investigate the effects of funnel-web spider toxin (FTX) and its synthetic analog (sFTX) on neuromuscular transmission.
- To identify the specific type of VDCC targeted by FTX and sFTX in motor nerve terminals.
- To determine the prevalence of P-type VDCCs in mammalian synapses.
Main Methods:
- Electrophysiological recordings of presynaptic currents at the mouse neuromuscular junction.
- Measurement of muscle contraction and neurotransmitter release evoked by nerve stimulation.
- Assessment of K(+)-induced Ca45 uptake by brain synaptosomes.
Main Results:
- FTX and sFTX abolished mammalian neuromuscular transmission, blocking muscle contraction and neurotransmitter release.
- Both toxins specifically blocked presynaptic Ca2+ currents in motor nerve terminals.
- FTX and sFTX inhibited K(+)-induced Ca45 uptake in brain synaptosomes, indicating P-type VDCC blockade.
Conclusions:
- The predominant VDCC in motor nerve terminals is the P-type channel.
- P-type VDCCs likely play a significant role in neurotransmitter release at a substantial percentage of brain synapses.
- FTX and sFTX are valuable tools for studying P-type VDCC function in the nervous system.