lec 4

Question 1

I= deltaV*G

Answer 1

deltaV= voltage diff across membrane= driving force

G= conductance (depends on open probability of channels)

Question 2

what two forces act on an ion when it moves?

Answer 2

electrical gradient

chem gradient

Question 3

difference between a skeletal and cardiac AP

Answer 3

cardiac has no tetany/summation due to long AP duration

100% recruitment of muscle fibers with every beat

Question 4

what happens to the Ca channel when diltiazem is added?

Answer 4

it is a Ca channel blocker

AP duration will decrease bc; decreased depolarizing Ica, decreased Ca entry, decreased force contraction

–> the plateau at the end will be shorter because Ca “wins”/repolarizes faster when Ca channels blocked

Question 5

Ikto

Answer 5

cardiac K+ current
(transient outward current)

-rapid early repolarization
- phase 1; rapid upstroke

Question 6

Ik1

Answer 6

cardiac K+ current
(inward rectifier)

• resting membrane potential and long plateau
• phase 4 and part of long plateau
  -more like a leak channel, not v gated

Question 7

Ikdr

Answer 7

cardiac K+ current
(delayed rectifier)

• phase 3, slow kinetics; slow to activate, late repolarization after plateau
• v gated

Question 8

rectification

Answer 8

when volatage-dependent conductance of ions thru a channel flows better in one direction than the other

Question 9

inward current=

Answer 9

positive ion moving into the cell

Question 10

inward rectifier=

Answer 10

allows inward current but not outward

Question 11

rectifier=

Answer 11

passes ions more easily than others

Question 12

The delayed rectifier current (Ikdr); 3 types

Answer 12

1) slow delayed recitifer- Iks (KvLQT1)
-slow slow

2) rapid delayed recifier - Ikr (hERG)
- fast slow

3) ultra rapid delayed recifier - Ikur (Kv1.5)
- very fast slow

Question 13

slow delayed recitifer- Iks: what is the current

Answer 13

KvLQT1

Question 14

rapid delayed recifier - Ikr: what current

Answer 14

hERG

Question 15

ultra rapid delayed recifier - Ikur: what current

Answer 15

Kv1.5

Question 16

compare the speeds of the 3 delayed rectifier currents to v gated K channels

Answer 16

Ikdr (all 3 types) are slow compared to v gated K channels but hey kick in at different speeds

Question 17

what type of current do delayed rectifiers pass?

Answer 17

only outward

“delayed bc slower than Na”

Question 18

what is the most important channel

Answer 18

delayed rectifier

(and most important for repolarization)

Question 19

without delayed rectifier, IV curve would

Answer 19

be a straight line

Question 20

physiological range of Vm

Answer 20

-80 to -40mV (the bump)

Question 21

Na+ channel

Answer 21

pseudotetramer
4 domains but only 1 alpha subunit per Na channel

Question 22

K+ channel

Answer 22

true tetramer
4 alpha subunits per K+ channel

Question 23

Ca2+ channels

Answer 23

pseudotetrameric
more like Nav channels
one alpha subunit per Ca2_ channel