Lecture 5 - Trandsuction Mechanism Flashcards
What do receptors located on the cell membrane have?
An extracellular domain, intracellular domain and transmembrane domain
Where do chemicals, drugs and transmitters bind?
On the extracellular site of the receptor
What are the types of post-synaptic effects?
Skeletal muslce - muscle membrane will be excited and fire action potentials and muscle will contract
Gland cell - will be exicted and secrete
Pacemaker cells - increase or decrease firing rate
Post-synaptic neurones - excited or inhibited in CNS
What are examples of cellular response?
Contraction, relaxation, secretion, growth, change in metabolism
What are type-1 receptors?
Ionotropic receptors which are part of ion channels. Their activation leads to the conductance of ions.
What type of neurotransmitters act on type-1 receptors?
Fast NT such as nicotinic acetylcholine
What is the response like in type-1 receptors?
Very fast e.g. milliseconds
What happens when a receptor binds to an ion channel?
At rest the channel is closed, when the agonist binds to the receptor, a change in conformation of the protein occurs which opens the ion channel. The ions flow through the pore down their electrochemical gradient.
Explain the example of Acetylcholine
Acetylcholine is the transmitter in the body at the skeletal NMJ and it binds to nicotinic receptors. It opens the channel for 1-2ms and causes an increase in Na+ and K+ ions, this inward current carried by the Na+ depolarises the cell membrane, this causes a release of Ca 2+ from SR. The Ca2+ binds to troponin C which leads to the activation of myosin ATPase and contraction of skeletal muscle.
What does a typical ionotropic receptor consist of?
5 protein subunits (each consisting of 4 alpha helices) forming a transmembrane structure with a central pore
What does the nicotinic receptor have?
The central pore carries a negative charge so only postive cations can flow through when the pore is opened
What happens when Ach binds to the nicotinic receptor?
The top region of the protein has a binding site for Ach, when Ach binds it changes the conformation of the protein, so the pore opens.
