Session 4 - Cellular + Molecular Events In The CVS Flashcards
What causes the upstroke of rapid polarisation in the SA node?
Opening of the voltage gated calcium ion channels resulting in a large influx of calcium into the cell
What are HCN channels?
Hyperpolarisation Cyclic Nucleotide-gated channels
The more negative the membrane potential the more activation of channels resulting in a quicker AP
What causes the rapid upstroke in ventricular APs?
A rapid influx of sodium ions into the cells
What causes the plateau of membrane potential in cardiac APs?
Influx of calcium as L-type Calcium ion channels open balanced with Potassium efflux
How is excitation and contraction coupled in cardiac muscle?
- AP travels down T-tubule and causes L-type Calcium ion channels to open allowing calcium into the cell
- this calcium can then bind to Calcium Induced Calcium release receptors to allowing more calcium into the cell from the SR
- This then binds to Troponin C allowing muscle contraction
- To stop stores depleting, they are pumped back into the SR by SERCA
Why is Mysoin light chain Kinase important in smooth muscle contraction?
It phosphorylates the myosin light chain, activating it and allowing it to bind to actin and contract?
What does MLCK require to become activated?
Calmodulin with calcium bound
How does noradrenaline cause an increase in contraction in smooth muscle?
It activates PKC which inhibits MLCP - which dephosphorylates the Mysoin light chain
Noradrenaline also causes IP3 to be released which increases calcium release into the cell and hence contractions increase
What does PKA do in terms of smooth muscle contraction?
Inhibits it, it phosphorylates MLCK which inhibits its action
In the SA node what is the ‘funny current’?
An influx of sodium ions which slowly depolarises the cells
What causes the downstroke in cardiac action potentials?
Opening of voltage gated potassium channels causing rapid efflux of potassium from the cell
