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Tetrodotoxin-sensitive protein in the extracts from excitable tissues
Biochimica Et Biophysica Acta
|May 21, 1982
Summary
Researchers identified a heat-inactivated protein in brain and heart tissue extracts that increases liposome sodium permeability. This effect, sensitive to tetrodotoxin, suggests a soluble precursor for voltage-dependent sodium channels.
Area of Science:
- Neuroscience
- Biochemistry
- Molecular Biology
Background:
- Voltage-dependent sodium channels are crucial for nerve impulse transmission.
- Understanding the molecular precursors of these channels is vital for neuroscience research.
- Soluble factors influencing ion channel activity are not fully characterized.
Purpose of the Study:
- To investigate soluble factors from excitable tissues that modulate liposome sodium permeability.
- To characterize the nature of the substance responsible for veratrine-induced sodium influx.
- To determine if this factor is related to voltage-dependent sodium channels.
Main Methods:
- Liposomes were incubated with soluble fractions of brain and heart homogenates.
- Sodium permeability was assessed by veratrine-induced ion flux.
- The effect of tetrodotoxin on veratrine response was evaluated.
- Proteolytic treatment (pronase) and heat denaturation were used to assess factor stability.
- Fractionation techniques including ammonium sulfate precipitation, DEAE-Servacel chromatography, and Sephadex G-200 gel filtration were employed.
Main Results:
- Veratrine increased sodium permeability in liposomes preincubated with brain and heart extracts.
- Tetrodotoxin significantly reduced this veratrine-induced increase in permeability.
- The observed effect was specific to extracts from excitable tissues (brain, heart), not liver or serum.
- The active factor was inactivated by pronase and heat, indicating a protein nature.
- The tetrodotoxin-sensitive factor eluted at the void volume of Sephadex G-200, suggesting a large molecular size.
Conclusions:
- A soluble, heat-labile protein factor present in excitable tissues enhances liposome sodium permeability in a tetrodotoxin-sensitive manner.
- This factor may represent a soluble precursor or component involved in the formation of voltage-dependent sodium channels.
- Further characterization could elucidate novel mechanisms in sodium channel biogenesis and regulation.