Structure of Voltage-gated Ion Channels

The dotted line indicates the location of the ion pore, a) Na channel b) Ca channel c) K channel. According to CatteraU, (1995) with permission. 

The large subunit is generally capable of forming an ion pore alone. In the large sub-imits of the Na and Ca charmels, four homologous domains can be identified that each have six potential transmembrane helices. The large subimit of the charmel has only one of these domains. Despite this, it fits into the structural principle of the Na and Ca channels since the large subunit is present as a tetramer. 

The associated subimits often have a stabilizing effect on the pore formed by the large subimit and they determine the details of activation and deactivation of the pore to a large extent. Furthermore, the associated subunits have phosphorylation sites and it is assumed that these can have a regulating effect on pore function. 

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