Shared Flashcard Set


Physiology Receptors and Secondary Messengeres

Additional Physiology Flashcards




Ligand-gated ion channels
• binding domain on receptor which opens or closes by binding ligand
• Roles and functions
o motor nerves (ACh acting on nicotinic receptors)
 Excitation: Na+ influx
 Inhibiton: Cl- influx
o autonomic nervous system (ACh acting at nicotinic receptors for conduction)
o CNS neurotransmission
 Excitatory: glutamate & nicotinic receptors; cation (Na+/K+) channels
• NDMA: highly permeable to Ca2+ too; two-signals needed (glutamate and glycine)
 Inhibitory: GABA & glycine receptors; Cl- influx
o CNS neuromodulation
 Nicotinic receptors mediate transmitter release
 NMDA receptors: coincidence detectors, synaptic “learning”
• Made of multiple protein subunits that form channels
• Ligands: Excitatory: ACh, Glutamate, Serotin; Inhibitory: GABA and Glycine
• Rate: fastest
G-protein coupled receptors
• Roles and functions
o mediate synaptic, endocrine, and paracrine
o wide variety of signals transduced: neurotransmitters, peptides, hormones, sensory (light, odorants, taste), adhesion, developmental proteins, chemokines, growth factors
• single gene product which spans the membrane 7 times
o 3 intracellular loops and one intracellular carboxyl tail
• Ligands
• Rate: slower than LGIC
Intracellular steroid
• Binding domain associated with DNA-binding domain
• Can cross plasma membrane – receptors are inside the cell
• In resting state, steroid hormone receptors bind to an inhibitory protein
• Binding of steroid ligand alters receptor conformation – releases protein inhibitor
• After release, interacts with DNA to create primary then secondary gene products
Enzyme linked
bind growth factor which promotes receptor dimerization--dimerization triggers auto-phosphorylation--activation of GTP-bound Ras--phosphorylation cascade
Three components of GPCR
 Three subunits: alpha, beta, and gamma (trimeric); there is a monomeric form (Ras)
• Alpha subunit: αi, alpha s, alpha q, alpha 12
• GDP at rest : bound to a, b, and g protein
• GTP when activated: alpha subunit breaks free from beta and gamma subunits; this form can bind target
 Can act as molecular switches
• GTP on
• GDP off
Secondary message systems
 adenylyl cyclase
• binding of GTP (alpha s) creates cAMP (2nd messenger)
• cAMP binds to inhibitory subunit on protein kinase A (PKA)
• activated PKA phosphorylates substrates – phosphorylation cascade
 phospholipase C-beta
• binding of GTP (alpha q) creates activated phospholipase C (PLC)
• PLC acts on PIP2 to create DAG (diacylglycerol) which stays in membrane and IP3 (inositol 1,4,5-triphosphate) enters cytosol
• DAG stimulates protein kinase C (PKC) – phosphorylation cascade; IP3 opens a channel in ER to release Ca2+, which regulates the activity of many proteins (one is PKC – Ca enhances)
On-and-Off signals
o On:
 electrical excitation
 sensory input and/or change in the cell environment
 other signals
 metabolic and/or genomic activity
o Off
 destruction of signal molecule
 removal of molecule: removal of phosphate from GTP
 plasticity of target
• receptor sequestration
• receptor down-regulation
• inactivation of signaling protein
• production of inhibitory protein
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