CV drug explanations/funny current/EC coupling

Question 1

What sympathetic effects does noradrenaline have on funny current

Answer 1

Increases I(Na) going into cells - increased rate
Increases I(Ca) in cells - increased contractility
Increases I(K) out of cells - delayed rectifier shortens AP - increased rate

Question 2

Funny current

Answer 2

Net Na in and K out

Question 3

What is the reversal potential of I(f)

Answer 3

-10mV

Reverse potential point at which there is no net movement in or out cell

Question 4

What controls the slope of the pacemaker potential

Answer 4

HCN channels

Na/Ca exchange

Question 5

Parasympathetic control of funny current

Answer 5

Ach increases K+ going out of ACh sensitive K channels - IK(ACh) (muscarinic) - hyperpolarises membrane, decreases slope of pacemaker potential

Question 6

Threshold potential in a cardiac myocyte

Answer 6

-50mV

Question 7

Inward rectifier channels (neural AP)

Answer 7

Transport K+ into the cell
Open when potential is less than -60mV (as hyper polarisation begins)
Stay open to keep membrane at rest

Question 8

Delayed rectifier channels (neural AP)

Answer 8

Transport K+ out of cell
Open when membrane depolarises
Are slow to close (results in hyperpolarisation)
When they close, it stops K+ leaving the cell - cell goes to resting potential

Question 9

When is Na+ permeability low (in a neural AP)

Answer 9

During repolarisation and hyperpolarisation

Question 10

What structures store and release calcium

Answer 10

T tubules and terminal cisternae

Question 11

What are T tubules

Answer 11

Invaginations in the membrane wall, next to the SR

So membrane currents can be near contractile machinery

Question 12

What is the terminal cisternae

Answer 12

An enlarged area of the sarcoplasmic reticulum

Stores and releases calcium

Question 13

T tubules and terminal cisternae mechanism

Answer 13

T tubule depolarises
Terminal cisternae detects it
Terminal cisternae sends it throughout SR
Huge increase in cytosolic calcium follows (released from SR)
Leads to contraction

Question 14

What is excitation contraction coupling

Answer 14

The link between the depolarisation of the membrane and the massive influx in intracellular calcium which causes the cell to contract

Question 15

Cause of calcium influx in skeletal muscle (EC coupling)

Answer 15

Membrane depolarises -> membrane ca channels undergo a conformational change -> calcium release channels in the SR (RyR) undergo a conformational change that opens them -> calcium flows into cytosol

Question 16

Cause of calcium entering cytosol in cardiac myocytes (EC coupling)

Answer 16

Ryanodine receptor triggered by small intracellular calcium increase
Positive feedback loop - more and more calcium released from SR

Question 17

SERCA

Answer 17

In SR membrane
Pumps Ca2+ back into SR (requires ATP)
Sympathetic stimulation -> increased EC coupling, which may cause calcium overload