093014 electrophysiology

Question 1

in non pacemaker cells of heart, what is responsible for the rapid upstroke of the action potential?

Answer 1

sodium entry-phase zero

Question 2

calcium enters cell through calcium channel during what phase of muscle cell AP?

Answer 2

2

Question 3

what contributes to the resting potential (phase 4) of nonpacemaker cells?

Answer 3

potassium

Question 4

funny channel or HCN is activated during when

Answer 4

hyperpolarization in pacemaker cell–turned on by repolarization of membrane potential and you get increase in sodium conductance

Question 5

after the inactivation gate on a sodium channel closes, what enables the activation gate to close and the inactivation gate to reopen again?

Answer 5

repolarization-as high negative membrane voltages are reachieved

Question 6

resting potential of cardiac muscle cell is determined by

Answer 6

balance btwn concentration gradient and electrostatic forces for potassium b/c only potassium channels are open at rest

Question 7

equilibrium potential of cardiomyocyte

Answer 7

-90mV

Question 8

what is the major current passing through gap jxn in cardiomyoctyes?

Answer 8

Na+ current–spreads depolarization to neighboring cells

Question 9

what contributes to the electrical delay btwn SA and AV nodes?

Answer 9

slower spread of depolarization by Ca2+ to neighboring cells

Question 10

what can decreases pacemaker rate and slow conduction rate through AV node?

Answer 10

G protein activated K+ current (an inward K+ current mediated by GIRK K+ channels and regulated by acetycholine)

Question 11

when is the If channel activated?

Answer 11

by hyperpolarization during phase 3 in pacemaker

Question 12

delayed rectifier channels

Answer 12

allow potassium to flow out of cell and causes you to see the repolarization in phase 3 of cardiac cell AP

Question 13

why is the SA node the dominant pacemaker?

Answer 13

because its cells have the fastest intrinsic spontaneous depolarization. normal resting rate sinus rhythm of 60-100 bpm

Question 14

when does calcium influx occur in pacemaker action potential?

Answer 14

phase zero-once Na+ allows for reaching of threshold

Question 15

why is upstroke of phase zero less rapid than in nonpacemaker cells?

Answer 15

because the current represents calcium influx through the relatively slow calcium channels

Question 16

speed of action potential upstroke divides cardiac cells into two types

Answer 16

slow response cells (SA, AV nodal cells)

fast response cells (atrial and ventricular myocytes, Purkinje cells)

Question 17

compare conduction velocities for fast response and slow response cells in heart

Answer 17

slow response has slow conduction velocity

fast response has faster conduction velocity

Question 18

resting membrane potential of slow response cell

Answer 18

-40 to -70 mV

Question 19

what causes spontaneous depolarization in SA node?

Answer 19

pacemaker channels (HCN channels)

these channels are modulated by ANS (Ach activates Gi inhibitory unit, so suppresses cAMP, so slow down or close off the channel)

Question 20

Ito K+ channel

Answer 20

for early outward K+ current in atrial and ventricular cells. contributes to phase 1

Question 21

effect of Ach on SA node

Answer 21

decreases If current, reducing steepness of phase 4

opens GIRK channels, increasing K+ conductance and making the diastolic potential more negative

reduces calcium current, reducing the steepness of phase zero and moves threshold to more positive value

Question 22

norepinephrine effect on heart

Answer 22

increases calcium current, increases calcium influx, increases ca induced ca release from SR–so INOTROPIC EFFECT

increase If, increases ICa

Question 23

mechanisms for altering heart rate

Answer 23

decrease rate of depolarization
decreas maximum diastolic potential
decrease calcium channel activity-changes upstroke of phase zero

Question 24

effect of beta adrenergic/cholinergic on SA node

Answer 24

conduction velocity

pacemaker rate

Question 25

cholinergics have little effect on what part of the heart?

Answer 25

atrial and ventricular muscle

Question 26

effect of resting potential on speed of depolarization in muscle cardiac cell

Answer 26

if you have more inactivated sodium channels (so higher resting potential), then you have have a slower speed of depolarization

Question 27

calcium channel blockers do what

Answer 27

decrease contractility of heart muscle

decrease entry of calcium and delay depoloarization of SA and AV nodal cells

Question 28

beta blockers do what

Answer 28

prevent calcium entry into the cell–decreases heart rate, conduction velocity and strength of contraction