Drugs and the Cardiovascular System – The Heart Flashcards
What is the major store of calcium within the cardiomyocyte?
Sarcoplasmic reticulum
The heart has two signalling pathways that are involved in elevating the level of two intracellular second messengers. What are these second messengers?
Ca2+ and cAMP
Which plasma membrane proteins allow calcium to enter the cell in response to depolarisation?
Dihydropyridine receptors
What happens to the calcium once it has passes into the cell viathis channel?
It binds to ryanodine receptors on the sarcoplasmic reticulum and cause calcium release from the SR
How does the calcium stimulate contraction?
It binds to troponin on the thin filament
What are the different ways in which calcium is removed from the myoplasm after it has stimulated contraction? Which method is responsible for the majority of calcium removal?
Plasma membrane calcium ATPase
Na+/Ca2+ exchanger
SERCA2a (sarcoendoplasmic reticulum calcium ATPase) –responsible for >70% of calcium removal
What features of contraction is SERCA2a responsible for andwhy?
Rate of calcium removal and so it’s responsible for the rate of cardiac muscle relaxation
Size of calcium store, which affects the contractility of the subsequent beat
What regulates the action of SERCA2a and how does it do this?
Phospholamban (PLN)
Phospholamban phosphorylation is stimulated by beta-adrenergic activity
It is a target for phosphorylation by protein kinase A
When dephosphorylated it is an inhibitor of SERCA2a
When phosphorylated it dissociates from SERCA2a and activates the Ca2+ pump
As a result, the rate of cardiac relaxation is increased and, on subsequent beats, contractility is in proportion to the elevation in the size of the SR calcium store
What is phospholamban dephosphorylated by?
Protein phosphatase 1
What are the three main channels that are responsible for the action potential in the sinoatrial node?
If channel – hyperpolarisation-activated cyclic nucleotide-gated (HCN) channel Calcium channel (T and L type) Potassium channel
Describe how these channels are responsible for the action potential of the sinoatrial node.
If channel is a sodium channel that opens at the most negative membrane potential
Opening of the sodium channel causes sodium influx, which begins to depolarise the membrane and stimulates the opening of calcium channels, which further depolarises the membrane
Potassium channels are responsible for repolarisation
What are beta adrenoceptors coupled with?
Adenylate cyclase – it increases cAMP, which is important in the opening of the If channel to begin depolarisation
How does the parasympathetic nervous system affect heart rate and contractility?
It is negatively coupled with adenylate cyclase
What are the determinants of myocardial oxygen supply?
Arterial oxygen content
Coronary blood flow
What are the determinents of myocardial oxygen demand?
Heart rate
Contractility
Preload
Afterload
What effect do beta-blockers and calcium channel blockers haveon the channels responsible for the SA node action potential?
Beta-blockers decrease If and calcium channel activity
Calcium channel blockers only decrease calcium channel activity
Name a drug that decreases If activity.
Ivabradine (blocks the If channel)