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  1. Introduction
  2. The relation between primary protein structure and ion channel function
  3. Toxins isolated from the buttercup family
  4. Potassium (K+) channels
  5. Delayed rectifier channels
  6. M channels
  7. KATP channels
  8. Calcium (Ca2+) channels
  9. Chloride (Cl?) channels
  10. Conclusion
  11. References

Structure and Function of Voltage-Gated Ion Channels Voltage-gated ion channels allow the flow of ions in response to changes in membrane voltage and are key elements in neuronal excitation and inhibition. Although ion channels can usually pass more than a single type of ion, voltage-gated channels are named according to the predominant ion that flows when the channel is open. Ion channels that are selective for Na+, K+, Ca2+, or Cl? have been described in neuronal membranes. Certain ion channels that are gated directly by chemical neurotransmitters such as glutamate and acetylcholine are selective for Na+, K+, and Ca2+ but exclude Cl? and are called nonselective cationic channels.

[...] Cloning studies of channels from Shaker indicate that some channels, like Na+ channels, are proteins that have six putative membrane spanning regions (S1 through a reentrant p loop between S5 and S6 that lines the ion channel pore, and a voltage sensor in the S4 region. These channel proteins are only about one fourth the size of the Na+ channel a-subunit and have only one of the homologous internal repeats seen in Na+ channels. It also appears that there are multiple distinct subfamilies of channels based on genetic studies in Drosophila, where the most detailed analysis has been done. [...]

[...] Some ion channels are opened by hyperpolarization instead of depolarization. These include anomalous (inward) rectifier and H channels that allow to enter rather than exit the cell. The name ?anomalous rectifier? (also called ?inward rectifier?) indicates that, in contrast to the delayer rectifier, this channel passes much better in an inward than in an outward direction. The anomalous rectifier and H channels (hyperpolarization activated channels) are believed to contribute to the neuronal resting membrane potential and to pacemaker firing in certain neurons. [...]

[...] These G?protein?regulated, inwardly rectifying channels (GIRKs) allow divergent synaptic inputs to a single neuron to exert regulatory influences over neuronal firing through a single class of ion channels. The inwardly rectifying channels, including KATP channels, differ structurally from the Kv (Shaker) family described previously in that they have only two membrane spanning regions and a pore-forming loop; GIRKs also lack the voltage sensor found in the Kv family. KATP channels appear to be heteromultimers that contain an inwardly rectifying channel and a large subunit that binds ATP and sulfonylurens. [...]

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