Metabotropic Receptors: Second Messengers Systems

How do metabotrophic receptors affect neuronal activity

Altering Ca2+ channel function

Altering K+ Channel Function

Releasing Ca2+ from intracellular stores

Altering presynaptic active zone protein function (probability of release)

Alterations in postsynaptic receptor sensitivity

True or False: Metabotropic Receptors are activated by multiple NT which activate numerous pathways

True

External Signal(First Messenger)

Neurotransmitter

Transducer

G-proteins(a,B, y- molecular switch)

Primary Effector

First Protein that a-GTP or B-y dimers bind to

Describe the Direct Pathway

NT Acteylcholine—>binds to mACHr—>activates G b-y protein which acts on K+ Channels

Describe the cAMP Pathway

NT Norepinehphrine—>binds to B-adrenergic receptor—>activates Gs protein which acts on Adenyl Cyclase which activates cAMP to activate PKA

Describe the Phosphinositol Pathway

NT Acetycholine—>binds to Muscarinic Ach receptor—>activates Gq protein which acts on PLC which cleaves PIP2 to make IP3(responsible for Ca2+) and DAG(combined with Ca2+ activates PKC)

Describe the Arachidonic Acid Pathway

NT Histamine—>binds to Histamine receptor—>activates Gi/o protein which acts on PLA2 which activates the arachidonic acid to activate (5-Lipoxygenase,12-Lipoxygenase,Cyclooxygenase)

How did experimenters show which G-protein is involved in modulating GIRK channels

Experimenters put different G-protein constituents and tested for current

-A-B-y: no GTP

a-B-y+GTP-y-S: curret occured but don’t know which it is

a-GTP: no current occured

B-y(no GTP): Current occurred

What was a second way that experimenters determined which G-protein stimulated GIRK channels

They injected mRNA for GIRK Channels and G-proteins,waited 2 days for protein expression,a and recorded current from GIRK+ B,y proteins

IDK=FIX

How did experimenters prove that PKA increases calcium current by increasing the probability of channel opening

Blocked by PKA inhibitors

Mimicked by activators of PKA, adding catalytic subunit of PKA or cAMP itself

Purified channels in lipid bilayer to record single channel events

Add PKA/ATP show increased p(open), then run gel to show phosphorylation of channel

Evidence demonstrating indirect pathway involvement in G-protein mediated effects FIx

Use a PKC activator(oleoylacetylglycerol OAG) inhibits N-type calcium current\

• Look for additive or occlusve effects= Effect of NE is blocked by PKC inhibitor(PKCl 19-31)

• So, NE likely works through PKC pathway

How can GPCR exhibit specificity

Signaling Cascades can be spatially restricted,

Whole cell dialysis does not affect inhibition

Cell attached recordings don’t show inhibition when transmitter is added to the outside