Sodium channels are central to a host of fundamental cellular processes, including sensory perception, pain, and muscle contraction. In order to understand any of these processes in detail, it is necessary to know the atomic structure of the channel proteins both with and without bound sodium ions. In this issue, Naylor et al (2016) present the structure of a bacterial sodium channel tetramer. The three bound, partially hydrated sodium ions line up neatly in a row inside the selectivity filter, providing us with the first detailed insights into ion conduction in sodium channels, and the mechanisms by which sodium and potassium ions are discriminated.
See also: CE Naylor et al
Ion channels that conduct sodium, potassium or calcium ions through the lipid bilayer of the membrane play a central role in cellular physiology. Sodium channels are key components of electrically excitable cells, where they contribute to the neuronal action potential and sensory perception, including vision, hearing and pain. These channels have been subject to countless investigations ever since Hodgkin and Huxley first published their classical studies of sodium and potassium conductance in the squid giant axon (Hodgkin & Huxley, 1952). Famously, sodium channels are blocked by spider and scorpion toxins that paralyse or kill prey. They are of great pharmacological importance as key targets for local anaesthetics, anti‐epileptic drugs and compounds to treat cardiac arrhythmia.
The lipid bilayer of biological membranes is electrically insulating. Most ions cannot pass through it unaided, or can do so only very slowly. Ion channels are passively conducting protein pores that lower the free energy barrier to ion permeation. Most channels specifically conduct one, and only one type of ion. The difference in ion concentration within and outside a cell creates the membrane potential as one of the defining features of life. Permanently open channels will …
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