Study Set Content:
a ligand-gated ion channel.
nicotinic
acetylcholine (ACh) receptor,
The nicotinic
acetylcholine (ACh) receptor,
a ligand-gated ion channel.Composed
of five subunits
(two α, one
β, one γ, and one δ),
the
receptor opens a (blank)
when ACh binds to sites on
the extracellular domain of
its α subunits.
central
transmembrane ion channel
do not bind neurotransmitters
directly but are controlled by membrane potential; such channels
are also important drug targets.
Voltage-gated ion channels
For example, (blank) inhibits voltage-gated calcium channels,
that are present in the heart and in vascular smooth muscle,
producing antiarrhythmic effects and reducing blood pressure
without mimicking or antagonizing any known endogenous
transmitter.
verapamil
Receptors coupled to G proteins are often called:
“G protein-coupled receptors” (GPCRs), “Seven-
transmembrane” (7-TM), “heptahelical” receptors, or
“Serpentine” receptors.
Protein located in the cell membrane that binds extracellular
substances and transmits signals from these substances to an
intracellular molecule called a
G protein
GPCR’s make up the largest receptor family and are so-named
because the receptor polypeptide chain (blank) across the plasma
membrane (blank) times.
“snakes”, seven
Many extracellular ligands act by increasing the
intracellular
concentration of second messengers
Many extracellular ligands act by increasing the intracellular
concentration of second messengers such as
Cyclic adenosine-3’,5’ monophosphate (cAMP)
o Calcium Ion
o Phosphoinositides
After reaching an initial high level, the response (eg. cellular
cAMP accumulation, Na + influx, contractility, etc.) (blank)
over seconds or minutes, even in the continued presence of
agonist.
diminishes
This “desensitization” is often rapidly
reversible
a second
exposure to agonist, if provided a few minutes after the
termination of the first exposure, results in a response similar to
the
initial response
B. Agonist binding to receptors
Step 1
Initiates signaling by promoting
receptor interaction with G
proteins (G’s) located in the cytoplasm
Step 2
Agonist-activated receptors are
phosphorylated
Step 2
Agonist-activated receptors are phosphorylated by a
G
protein-coupled receptor kinase (GRK),
Agonist-activated receptors are phosphorylated by a G
protein-coupled receptor kinase (GRK), preventing receptor
interaction with
G’s
Agonist-activated receptors are phosphorylated by a G
protein-coupled receptor kinase (GRK), preventing receptor
interaction with G’s and promoting binding of a to the receptor
different protein,
β-arrestin (β-Arr),
Step 3
The receptor-arrestin complex binds to (blank)
promoting receptor internalization.
coated pits,
Step 4
(blank) from internalized receptors reduces β-
Arr binding affinity,
Dissociation of agonist
