Action Potentials

Question 1

What is the funny current?

Answer 1

mediated by HCN gated channels - opened by hyperpolarisation and cAMP - conduct Na+ and K+ - facilitates slow phase 4 depolarisation

Question 2

What happens during phase 1 in myocytes?

Answer 2

brief repolarisation - K+ channels open briefly - K+ efflux

Question 3

What occurs during phase 4 in nodal tissue?

Answer 3

pacemaker potential, funny current, Na+ channels allow slight Na+ influx - background depolarisation, voltage activated T-type Ca2+ channels open briefly - occurs near threshold - final kick to reach threshold, K+ efflux in background - gradually reduced

Question 4

What is the mechanism of action of Ivabradine?

Answer 4

selective blocker of HCN channels - reduces slope of pacemaker potentials - slows HR

Question 5

What occurs in phase 0 in nodal tissue?

Answer 5

depolarisation - opening of voltage activated L-type Ca2+ channels - Ca2+ influx

Question 6

What occurs during phase 4 in myocytes?

Answer 6

resting membrane potential - background K+ efflux

Question 7

What is the function of the plateau phase in myocytes?

Answer 7

no additional AP can be fired during it - limits max HR - heart can function efficiently

Question 8

How do myocytes gain the Ca2+ to trigger contraction?

Answer 8

L-type channels slowly open during upstroke - Ca2+ influx

Question 9

What occurs during phase 2 in myocytes?

Answer 9

L-type Ca2+ channels open slowing during upstroke - generates depolarisation, K+ channels in background - K+ efflux - repolarisation , Ca2+ current that slowly inactivates = K+ current that slowly activates, small inwards Na+ current - important in the generation of arrhythmias

Question 10

What is the pacemaker potential?

Answer 10

net influx of positive charge that facilitates slow depolarisation

Question 11

What happens during phase 0 in myocytes?

Answer 11

depolarisation - voltage activated Na+ channels open - Na+ influx

Question 12

When does plateau occur?

Answer 12

phase 2 in myocytes

Question 13

What is Ivabradine used for?

Answer 13

slow HR in angina, reduced blood supply to cardiac muscle - angina pain due to lack of oxygen - slower HR reduces oxygen consumption

Question 14

Is Ivabradine a first or second line drug?

Answer 14

second

Question 15

What occurs in phase 3 in both myocytes and nodal tisuue?

Answer 15

hyperpolarisation - opening of voltage activated K+ channels - K+ efflux

Question 16

What is the resting potential of contractile myocytes?

Answer 16

-90mV