Related Experiment Videos
Actions of a polypeptide toxin from the marine snail Conus striatus on voltage-sensitive sodium channels
T Gonoi1, Y Ohizumi, J Kobayashi
1Department of Pharmacology, University of Washington, Seattle 98195.
Abstract:
The effects of a polypeptide toxin of 25,000 Da from the marine snail Conus striatus (CsTx) on sodium channels in mouse neuroblastoma cells and rat brain synaptosomes were studied. CsTx slowed sodium channel inactivation without altering the time course of activation of the channels. The voltage dependence of sodium channel inactivation was shifted to more negative membrane potentials and made less steep. Peak sodium currents were increased, and the voltage dependence of activation was shifted to more negative membrane potentials. The action of the toxin was voltage-dependent. Maximum toxin effects were observed at membrane potentials in the range of -100 to -60 mV. Apparent KD values were calculated assuming a one-to-one binding interaction. At more positive membrane potentials, the apparent KD for toxin action increased e-fold for each 19-mV depolarization. Apparent KD also increased at membrane potentials more negative than -100 mV. CsTx did not have significant effects on the binding of saxitoxin or Leiurus alpha-scorpion toxin to their receptor sites on sodium channels. CsTx enhanced the binding of batrachotoxinin A 20-alpha-benzoate to sodium channels in the same concentration range as its physiological effects. It is concluded that CsTx interacts with a new receptor site on the extracellular surface of the sodium channel at which specific effects on channel inactivation can occur.
Insights
A marine snail toxin, Conus striatus toxin (CsTx), alters sodium channel function by slowing inactivation and enhancing activation. This voltage-dependent toxin binds to a novel site on the sodium channel extracellular surface.
Area of Science:
- Neuropharmacology
- Ion Channel Physiology
Background:
- Sodium channels are crucial for neuronal excitability.
- Marine toxins are valuable tools for studying ion channel function.
Purpose of the Study:
- To investigate the effects of Conus striatus toxin (CsTx) on voltage-gated sodium channels.
- To characterize the binding site and mechanism of action of CsTx.
Main Methods:
- Electrophysiological recordings in mouse neuroblastoma cells.
- Biochemical binding assays using rat brain synaptosomes.
- Voltage-clamp analysis of sodium channel kinetics.
Main Results:
- CsTx significantly slowed sodium channel inactivation and shifted its voltage dependence to more negative potentials.
- The toxin increased peak sodium currents and shifted activation voltage dependence negatively.
- CsTx exhibited voltage-dependent action, with maximal effects between -100 and -60 mV.
- CsTx enhanced batrachotoxinin A 20-alpha-benzoate binding, suggesting interaction with a distinct receptor site.
Conclusions:
- CsTx interacts with a novel extracellular receptor site on sodium channels.
- This interaction specifically modulates sodium channel inactivation kinetics.
- CsTx represents a new pharmacological tool for probing sodium channel function.