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Potassium channels are crucial regulators of membrane excitability. They control the frequency and shape of action potentials, regulate secretion of hormones and neurotransmitters and establish cell plasma membrane potential. This large family can be regulated by voltage, Ca2+, neurotransmitters and the signaling pathways that they stimulate. Structurally, potassium channels exist as tetramers and the pore forming entity is the α-subunit. There are more than 70 different genes encoding the K+ α-subunit in the human genome.
The figure below shows the proposed structure of voltage-gated potassium channels.
A. A single α subunit showing the K+ ion selectivity signature motif 'T/SxxTxGYG' within the pore loop.
B. The general assembly of the K+ channel; composed of four, P loop-containing α-subunits arranged in a tetrameric fashion.
The table below summarizes the key characteristics of some potassium channels.
|Subtype||-||-||A-type||Delayed rectifier||Large conductance (maxi-K, BK)||Small conductance (SK)|
|Effect of Ca2+||Insensitive||Insensitive||Insensitive||Insensitive||Variable||High sensitivity|
|Effect of Voltage||Strong, inward rectification||Weak, inward rectification||Sensitive||Sensitive||Sensitive||Insensitive|
|Effect of ATP||Insensitive||Inhibits channel opening||Insensitive||Insensitive||Insensitive||Insensitive|
|Conductance (pS)||5-30||5-90||< 1-20||< 1-20||100-250||6-14|
Robertson et al (1997) The real life of voltage-gated K+ channels: more than model behaviour. TiPS 18 474. Mathie et al (1998) Voltage-activated potassium channels in mammalian neurons and their block by novel pharmacological agents. Gen.Pharmacol. 30 13. Vergara et al (1998) Calcium-activated potassium channels. Curr.Opin.Neurobiol. 8 321..