Potassium channel diversity

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• What are the features of a potassium channel?

They are crucial regulators of excitability.

• Present in all life forms from bacteria, ‘up’.

• They are the foundation upon which all other forms of neuronal excitation must be built: •

The potassium currents that they mediate set:

Action potential firing frequency

Action potential repolarisation

Action Potential Threshold

Resting Membrane Potential

After Hyperpolarisation.

Hogkin and Huxley Figured methods of repolarisation.

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Small depolarisation can trigger Na+ channels and they flood into the cell. This drives Membrane potential towards -45MV, this triggers further depolarisation opening K+ channels, K+ ios leave and drive MP toward Ek. This is how action potentials are repolarised.

Delayed rectifiers due to K+ ions being slower after responding to the Na+ influx. Less K+ allows for longer repolarisation, if there are more K+ ions the shorter the AP as it returns to Ek .

2 broad divisions of K+ Channels

‘Leak’ channels – (i.e. always open) – E.g. concerned with setting resting membrane potentials

• Inward rectifiers (KIR, KcsA)

• Tandem-pore, outward rectifiers (K2P)

‘Gated’ channels – (i.e. opened and closed) – concerned with repolarizing APs and controlling excitability

• Ligand-gated (cyclic nucleotide, G-proteins, Ca2+)

• Voltage-gated (Kv – delayed rectifiers)

There are 8 main Potassium channels.