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Effects of funnel web spider toxin on Ca2+ currents in neurohypophysial terminals
Abstract:
Funnel web spider toxin (FTX) is reportedly a specific blocker of P-type Ca2+ channels. The effects of FTX on the Ca2+ currents of isolated neurohypophysial nerve terminals of the rat were investigated using the 'whole-cell' patch-clamp technique. Both the transient and long-lasting Ca2+ current components were maximally elicited by depolarization from a holding potential equal to the normal terminal resting potential (-90 mV). Externally applied FTX inhibited the high-voltage-threshold, transient component of the Ca2+ current in a concentration-dependent manner, with a half-maximal inhibition at a dilution of approximately 1:10000. FTX also shifted the peak current of the I-V relationship by +10 mV. The long-lasting Ca2+ current component, which is sensitive to L-type Ca2+ channel blockers, was insensitive to FTX. The transient current, which is sensitive to omega-conotoxin GVIA, was completely blocked by FTX. These results suggest that there could be a novel, inactivating Ca2+ channel in the rat neurohypophysial terminals which is affected by both N-type and P-type Ca2+ channel blockers.
Insights
Funnel web spider toxin (FTX) specifically blocks a novel, inactivating Ca2+ channel in rat neurohypophysial terminals. This toxin affects transient Ca2+ currents, suggesting a new target for channel blockers.
Area of Science:
- Neuroscience
- Pharmacology
- Molecular Biology
Background:
- P-type Ca2+ channels are crucial for neuronal function.
- Funnel web spider toxin (FTX) is known to block P-type Ca2+ channels.
- Neurohypophysial nerve terminals release hormones regulated by Ca2+ influx.
Purpose of the Study:
- To investigate the effects of FTX on Ca2+ currents in rat neurohypophysial nerve terminals.
- To characterize the specific Ca2+ channel subtypes targeted by FTX in this preparation.
Main Methods:
- Whole-cell patch-clamp technique applied to isolated rat neurohypophysial nerve terminals.
- Application of varying concentrations of FTX.
- Analysis of transient and long-lasting Ca2+ current components.
Main Results:
- FTX inhibited the high-voltage-threshold, transient Ca2+ current component in a concentration-dependent manner (IC50 ~1:10000).
- FTX shifted the peak current-voltage relationship by +10 mV.
- The transient current, sensitive to omega-conotoxin GVIA, was completely blocked by FTX, while the long-lasting component (L-type sensitive) was unaffected.
Conclusions:
- A novel, inactivating Ca2+ channel exists in rat neurohypophysial terminals.
- This channel is sensitive to both N-type and P-type Ca2+ channel blockers.
- FTX serves as a valuable tool for characterizing this unique Ca2+ channel population.