Cardiac Myocytes AP

Phase 0 is rapid

depolarization from -90 mV → 20 mV

Why rapid depolarization in P0?

open v-gated Na+/Ca2+ channels
I(K+ - TO)

V-gated Ca2+ channels are not

long lasting, usually T-type channel

TO

transient outward

recitfying channels may/may not

contribute to phase 1

Phase 1 is short, imcomplete repolarization b/c

v-gated Na+/Ca2+ channel inactivated
repolarizing K+ current

transition state b/n

phase 2 and 3

transition state inactivates

L-type Ca2+ channel

Stopping Ca2+ channel in transition state

stops Ca2+ influx

Phase 4 is just

resting membrane potential

Phase 4 K+ efflux via

I(K-1)

I(K-1)

TASK, always opened

Phase 4 Na+ influx via

V-gated Na+ channel that occasionally opens

Phase 3 is the complete repolarization due to

L-type Ca2+ channel
I(K-1)
I(k-rapid) & I(K-slow)

Phase 3 L-type Ca2+ channel

inactivates completely preventing influx

Phase 1 rectifying channels create what currents

I(K-rapid) and I(K-slow)

Phase 1 Na+/Ca2+ channel is

inactivated at peak

Phase 1 repolarizing K+ current

flows thru K+ channel

Phase 2 is

slow repolarization phase

Phase 2 K+ efflux carried by

I(K-rapid) & I(K-slow)

Phase 2 dpolarizing Ca2+ carried by

L-type Ca2+ channel I(Ca-L)