Question

An action potential has reached the terminal bouton of the pre-synaptic neuron, calcium rushes in, allowing the release acetylcholine into the synaptic cleft. Acetylcholine then binds to a muscarinic receptor. Describe the nature of an ACH muscarinic receptor and the function of G-proteins in the action of these receptors. How does stimulation of these receptors cause the production of a hyperpolarization or depolarization in the postsynaptic cell?

Answer 1

The muscarinic acetylcholine receptor (metabotropic receptor) is a transmembrane protein that interacts with G-proteins. These receptors mediate most of the effects of acetylcholine in brajn. They contain binding sites for acetylcholine. Binding of acetylcholine to this receptor activates a G-protein which in turn opens a K+ channel. Opening of K+ channel allows a larger number of potassium ions to diffuse out of the cells and an inhibitory postsynaptic potential (IPSP) forms. Acetylcholine released at the inhibitory synapse causes a small hyperpolarization called IPSP. Diffusing out of more no. Of K+ ions creates a membrane potential which is more negative on inside as compared to resting state which makes the generation of action potential more difficult (during hyperpolarization).