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Ion Channel Proteins

Author: Scott A. Sheffield MS

Last update: Oct 6th, 2022

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The phospholipid bilayer forms a barrier that limits the passage of ions through the neuron cell membrane and separates the surrounding water environment into two compartments:

• the extracellular fluid (ECF) and
• intracellular fluid (ICF).

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• Ion channels are transmembrane proteins that allow small ions to move between the ECF and ICF without binding or using cellular energy.

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• The size, shape, and charge of each channel’s pore selectively allows only certain types of ions to pass.
• Some types of channels are functionally open most of the time and continually allow ions to diffuse through the selective pore.

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• K+ leak channels (in nerve and muscle cells) are examples. They allow K+ to flow out of the cell, which plays a major role in establishing resting membrane potentials.
• Other types of membrane channels have gates that usually block the flow of ions unless certain stimuli (chemical, voltage, mechanical, etc) are present.

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• When stimulated, the channel gates open and ions diffuse through the selective pore.
• Na+ and K+ voltage-gated channels (also in nerve and muscle cells) are examples. A change in voltage causes these channels to open and the exchange of ions produces an action potential (or impulse).