02

3

4

Slow Response

0 100 200 300

0 100 200 300

Diasto

lic Depo

larizat

ion

Threshold

CA PERMIABILITYK PERMIABILITY0mv

-60mv

-40mv

1 2

3

4

PLATEAU

K PERMIABILITY CA PERMIABILITY

PLATEAU

-90mv

0mv

Fast Sodium ChannelsResponsible for Depolarization

IK1 Inward Rectifying Potassium channel-High resting K+ Permeability

-Responsible for -90mv resting potential

ThresholdDiastolic Depolarization (DD) Decrease in K+ eux through Ikr + Iks channels -in Slow Response Fibers these progressivly close during DD Increase permeability to Sodium Sodium enters through If channels that open at -60mv Increase permeability to calcium L-type begin to open as membrane approaches threshold

Sodium Channel BlockerSlows rate of depolarizationSlows conduction VelocityTreats V-tach + A-b

Potassium Channel BlockerActs on IKr + IKsProlong the duration of APTreats: V-tach + A-Fib

Calcium Channel BlockerSuppresses activity of SA + AV node (Depolarization caused by calcium channels)-Slows rate of diastolic depolarization = slower HRTreats: Arrhythmias due to early and late afterpolarizaitonsAlsoDecreases cardiac contractility + SVR so used to treat Angina + Hypertension

Activation Gate

Inactivation GateInactivation

Gate

Activation

Gate

Na

Activation Gate

Inactivation Gate

Less than 1msLater Inactivation

Gate Closes

Activation Gate

Inactivation Gate

Fast sodium channelsopen and cause

Phase 0: Depolarization

Fast Sodium ChannelsReset to resting congurationas membrane potentialgoes from -50 -> -90mv

CC: pathological conditions existmembrane potentia does not repolarizeenough and inactivation gate does not reset, ber assumes SlowResponse characteristics

Inward rectifying Potassium ChannelCloses during Deplarization

Ik1 reopens at -40mvand contributes to lastphase of repolarization

K

Outward TransientRectifying Channel Ito1

Depolarization breiy opens these channel

They contribute to partialrepolarization (phase1)

K K

Outward Delayed Rectifying ChannelsIKr + Iks: Closed by depolarization

They determine the Beginning of Repolarization

Outward Delayed Rectifying Channels IKr + IKsClosed by depolarization

Ca

Ca

L-Type Calcium ChannelVoltage Gated, Opens at threshold

Open for a L-ong timeResponsible for plateau

Closes during repolarization

L-Type still open

L-Type Closes during Repolarization

K

K

Activation Gate

Inactivation Gate

K

Eective Refractory period last between Depolarization a half way through RepolarizationIt is caused by the INACTIVATION GATES of Fast Sodium Channels

IK1 Inward Rectifying Potassium channelare expressed at a much lower level in slow bersExplains -60mv resting potentialDO NOT OPEN IN SLOW FIBERS

Outward Delayed Rectifying Channels IKr + IKsContribute to DD in Slow Fibersby progressivle clossing

K KNa

Ca

If: Funny sodium ChannelsOpen when membrane reachesMaximum Negative potential(-60mv) and close approachingThreshold

Funny Sodium ChannelsClose at threshold

Fast Sodium ChannelsNon functional bc InactivationGate wont reset