Flashcards in Cellular And Molecular Events Deck (19):
What is the approximate value of Ek?
What is the approximate RMP of cardiac myocytes?
What values does the AP of the SAN change from and to?
-60mV to +30mV
What values does the AP of the ventricles change from and to?
-90mV to +30 mV
The plateau of a ventricle AP is caused by which ion channels?
L type voltage-gated calcium channels
Describe the phases of the ventricle AP
0: Na+ channels open to cause upstroke
1: transient outwards K+ current
2: plateau caused by opening of VG calcium channels
3: repolarisation due to inactivation of calcium channels and opening of VG K+ channels
What is the funny current?
The slow depolarisation caused by Na+ influx in the SAN
What causes the upstroke of AP in the SAN?
Opening of VG calcium channels
Cannot rely on VG Na+ channels as many will be in inactivated state due to the funny current
What channels ca the funny current and what is their full name?
Hyperpolarisation-activated, cyclic nucleotide-gated channels
Describe the micro-histology of cardiac muscle
Single, central nucleus
When muscle has contracted and we need to decrease intracellular calcium, where does it go?
Most is pumped into the SR (SERCA)
Some exits the cell (PMCA and NCX)
Where does contraction regulation occur in smooth muscle?
At the myosin head
How is contraction of smooth muscle initiated?
By phosphorylation of the myosin head
Which enzyme phosphorylates the myosin head and what regulates this enzyme?
MLCK enzyme (myosin-light-chain-kinase)
Regulated by calmodulin
How is calmodulin modulated?
By the intracellular concentration of calcium
What happens in smooth muscle cells when NA binds to alpha 1 receptors?
G alpha q receptors activated
Phospholipase C activated which makes IP3
IP3 binds to IP3 receptors on SR to induce calcium release
Calcium binds to calmodulin
Calmodulin regulates MLCK activity
MLCK phosphorylates the myosin head and contraction occurs
Which enzyme deactivates the myosin head?
How does the activation of alpha 1 receptors also prevent contraction? (Mechanism to stop it)
DAG created also by phospholipase C
PKC activates MLCP
Dephosphorylation of myosin head so contraction cannot occur