Sodium Channels

Walter Stühmer, Max‐Planck‐Institute for Experimental Medicine, Göttingen, Germany

Published online: May 2001

DOI: 10.1038/npg.els.0000127

Biological cells are surrounded by an electrical insulating membrane and have a negative intracellular potential. The energy required to generate this potential difference is efficiently obtained through metabolic energy, which establishes a gradient of ions across membranes. Nature has developed miniature batteries that use this gradient to generate a membrane potential in the form of molecules called ion channels. Sodium channels use the sodium ion gradient to generate positive membrane potentials. Furthermore, generation and conduction of the nervous impulse is based on ionic gradients, as is the generation of electrical discharges used by electric fish to stun their prey while hunting.

Keywords: excitability; ion channels; membrane protein

Figure 1. Electrocyte cells from the electric organ of Electrophorus electricus are represented before (a) and after stimulation (b). The protein at the top represents the sodium/potassium exchanger. Upon arrival of an action potential along the nerve axons, the neurotransmitter acetylcholine is released from the presynaptic vesicles. The acetylcholine causes the opening of the postsynaptic acetylcholine receptors. These are poorly selective and therefore cause a depolarization towards 0 mV. This initial depolarization causes the activation of the sodium channels located on only one side of the electroplax cells. The increase in permeability to sodium makes the transmembrane potential rise to about +50 mV on the left side of the cells. After inactivation of the sodium channels, the potentials return within a few milliseconds to the initial state.
Figure 2. Schematic structure of the sodium channel main subunit. The four internal homologous repeats are represented as domains 1 to 4. Each domain contains six putative transmembrane segments, S1 to S6. The S4 segment contains several positively charged residues. The special structure between segments S5 and S6 forms part of the ion-selective pore. The link between domain 3 and domain 4 is involved in inactivation.
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 References
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    Doyle DA, Cabral JM, Pfuetzner RA et al. (1998) The structure of the potassium channel – molecular basis of K+ conduction and selectivity. Science 280: 69–77.
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 Further Reading
    Gotter AL, Kaetzel MA and Dedman JR (1998) Electrophorus electricus as a model system for the study of membrane excitability. Comparative Biochemistry and Physiology 119A: 225–241.
    book Hille B (1992) Ionic Channels of Excitable Membranes, 2nd edn. Sunderland, MA: Sinauer Associates.

Related Sub-Topics:

Ion Channels | Membrane Proteins
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Article Title: Sodium Channels
 
How to Cite close
Stühmer, Walter(May 2001) Sodium Channels. In: eLS. John Wiley & Sons Ltd, Chichester. http://www.els.net [doi: 10.1038/npg.els.0000127]