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Clinical pharmacy 2024/2025 Level 2 Pharm D Physiology and Pathophysiology (MD303)
Cardiac Action potential [Cardiac electrophysiology]
cardiac muscle has Resting Membrane Potential = -90 mV ➔(inside more –ve than
outside by 90mv)
Cardiac action potential ➔ change in resting membrane potential caused by flow of ion
into or out of cell through Ion channel
Phase Mechanism
Rapid depolarization to +20 mV
Upstroke
Phase 0 Opening of Na channel → influx of Na+ into the
[Depolarization]
cell
Transient Outward K+ current & ➔ ↓ Na+ current
Phase 1 Repolarization Na channel closed
[Initial repolarization]
Long period of depolarized membrane potential
NB
Outward K+ current
Main repolarizing current is K
↑ Inward Ca+ current [Due to opening of L-type Ca
Phase 2 Plateau while for depolarization is Na,
channel] & both current are Equal ➔ responsible
for contraction is Ca
for contraction.
(Ca➔ increase activity of cell as whole)
↓ Inward Ca current decrease,
Phase 3 Repolarization
↑ Outward K current increase till -90 mV
Resting membrane Membrane potential fully repolarize & return to resting
Phase 4
Potential level
| P a g e 100
