Transmembrane potential of ventricular cells and its ionic mechanisms Resting Potential: -90 mV 2 Action potential 0 Phase 0: Depolarization Phase 1: Early phase of rapid E 20 repolarization 0 · Phase2: Plateau Phase 3: Late phase of rapid repolarization -80 4 Phase 4: Resting phase 100 50050100150200250 Time(msec)
Transmembrane potential of ventricular cells and its ionic mechanisms Resting Potential: -90 mV Action Potential • Phase 0: Depolarization • Phase 1: Early phase of rapid repolarization • Phase 2: Plateau • Phase 3: Late phase of rapid repolarization • Phase 4: Resting phase 16
The action potential of a myocardial pumping cell opyrightO The McGraw-Hill Companies, Ine Permission required for reproduction or display a Resting potential (-90mv) 口 K+ Channel leaking 0 Phase o ( upstroke of the action potential Time(s) a Threshold potential (-70mV) 10.0 a Opening of Nat channel(Na+ current is the largest current in the heart 51.0 a K+ Channel starts to close 0.15 0.30
◼ Phase 0 (upstroke of the action potential) Threshold potential (-70mV) Opening of Na+ channel (Na+ current is the largest current in the heart) The action potential of a myocardial pumping cell. Resting potential (-90mV) K 0 + Channel leaking K + Channel starts to close 17
Resting potential K equilibrium potential Nat-inward background current Electrogenic Nat-Kt pump Extracellular space [Na+] [C门 [KT Na/K pump dNa* Nongated Nongated Membrane K' channel A Na channel .单∥ ATP [Na] [A] Cytoplasm Cn [K+
• Resting potential – K+ equilibrium potential – Na+ -inward background current – Electrogenic Na+ -K+ pump 18
opyright e The McGraw-Hill Companies, Inc. Permission required tor reproduction or display 2 Phase 1 (rapid repolarization a Fast shut of nat channel a k*t current stays below the resting value 100 0.15 0.30 a Ca2+ channel starts to open ■ Phase2 10.0 a The long-lasting L-type Ca2 channel open and Ca2+ enters
◼ Phase 1 (rapid repolarization) Fast shut of Na+ channel K + current stays below the resting value ◼ Phase 2 1 2 Ca2+ channel starts to open The long-lasting L-type Ca2+ channel open and Ca2+ enters 19
ca in the sa and av nodes The inward Ca2+ is the current source for the upstroke depolarization ( Phase 0) There is no nat channels Their upstroke is slower than those in the cardiac muscle cells The speed of the conducted action potential is much slower that that of any other cardiac tissue This feature in the av node leads to an electrical delay between atrial contraction and ventricular contraction
ICa in the SA and AV nodes • The inward Ca2+ is the current source for the upstroke/depolarization (Phase 0). • There is no Na+ channels. • Their upstroke is slower than those in the cardiac muscle cells. • The speed of the conducted action potential is much slower that that of any other cardiac tissue. • This feature in the AV node leads to an electrical delay between atrial contraction and ventricular contraction. 20