Receptors

Question 1

Intracellular signaling of beta receptors

Answer 1

**Stimulation of adenylyl cyclase and increased conversion of ATP to cAMP and stimulating a cascade that results in activation of glycogen phosphorylase.
Adenylyl cyclase is activated by Gs coupling protein

Note: in the heart, activation of cAMP synthesis increases influx of calcium and its sequestration in the cell

Question 2

intracellular signaling of alpha-1 receptor

Answer 2

Phospholipase C hydrolyzes polyphosphoinositides and leads to formation of IP3 and DAG
IP3 promotes release of intracellular sequestered calcium and activation of calcium-dependent protein kinases which then increase the influx of calcium across the cell membrane.
DAG activates protein kinase C

Question 3

intracellular signaling of alpha-2 receptor

Answer 3

Activation causes inhibition of adenylyl cyclase decreasing cAMP.
Inhibition is transduced by inhibitory regulatory protein Gi

Question 4

Direct cardiac effects of muscarinic agonists (M2)

Answer 4

1. increase in the potassium current in SA & AV nodes, Purkinje cells, atrial and ventricular muscle cells
2. decreases the slow inward calcium current in heart cells
3. reduces the “funny” current