In the last article we looked at G-protein coupled receptors. Now, we will be going over the another main type of cell receptors: ion channel receptors.
Introduction
Ligand-gated ion channel (LGICs) receptors are found especially in excitable cells, and are responsible for changing the potential gradient (the difference of charges between intracellular and extracellular spaces). Excitable cells are cells that can communicate through electrical signals to each other by changing the potential gradient, for example neurons. (Miura, R. M. (2002, July 1). Analysis of excitable cell models. ScienceDirect. https://www.sciencedirect.com/science/article/pii/S0377042701005507) This is because a flow of ions from one place to another causes electrical currents (Crash Course. (2015, March 2). The Nervous System, Part 2 – Action! Potential!: Crash Course A&P #9 [Video]. YouTube. https://www.youtube.com/watch?v=OZG8M_ldA1M). A change in the potential gradient will also initiate cellular responses (Osmosis Youtube. (2020, October 14). Common cell signaling pathway [Video]. YouTube. https://www.youtube.com/watch?v=9sF_h-bAnIE).
Structure and Mechanism
LGICs are transmembrane ion channels with receptors, made up of four or five protein subunits, forming a tunnel through the membrane of cells. (Absalom, N. L. (2004, March 1). Mechanisms of channel gating of the ligandâgated ion channel superfamily inferred from protein structure. The Physiological Society. https://physoc.onlinelibrary.wiley.com/doi/10.1113/expphysiol.2003.026815）When the receptor is inactive, the ion channel is closed, separating extracellular and intracellular space. As the LGIC binds to a ligand, its structure changes and the ion channel opens up, allowing ions, Na+, K+, Ca++, or Cl− , to move into the cell before going back out. (Md, V. R. S., PhD, & Ramachandran, V. S., MD PhD. (2002). Encyclopedia of the Human Brain (1st ed.). Academic Press.) This happens within a few milliseconds.
LGICs can also be activated by G-protein coupled receptors, where the G-proteins trigger the LGIC to open up. (Neuroscientifically Challenged. (2014, September 27). 2-Minute Neuroscience: Receptors & Ligands. YouTube. https://www.youtube.com/watch?v=NXOXZ-kaSVI)
