Physiology of the Heart

Daniel HodycDepartment of Physiology

UK 2.LF

1. Action potential in myocardium

2. Prapagation of AP, arrythmias

3. Excitation - contraction coupling

Physiology of the Heart

Action potential in myocardium significantly differs from AP in skeletal muscle or nerve

Skeletal muscle,nerve Myocardium

The origin of different shape of AP curve is in voltage gated L-type calcium channels

Ca ions influx strongly influences the strenght and duration of myocardial

contraction

Katecholamines- beta-receptor on the cardiomyocyte membrane- adenylalcyclace, cAMP- activation of L-type Ca channels

Acetylcholine- muscarine receptors- adenylatcyclase inhibition

Plasmatic concentration of Ca

Ca channels

action potential duration

force of contraction

treatement of congestive heart

failure

???

Effect of Ca-channel blockers (Verapamil, nifedipin)

Longer AP prevents the tetanic contraction in myocardium

The length of plato phase in influenced by K+ channels and differs in various parts of

myocardium

Greater activity of K+ channels in atrium causes shorter plato phase

Atrial myocardium Ventricular myocardium

Hypercalemia causes higher excitability and leads to arrythmias

AP differs in normal myocardium and conductive sytem

Ventricular myocardiumConductive system - SAN

AP in SAN is caused by different channels

Na - „funny channels“

Ca - channels

K+ channels

Effect of acetylcholine on heart frequncy

Slower depolarization

Hyperpolarization

Spreading of the AP in the heart

Reentry mechanism

Excitation-contration coupling - initiation fo the contraction

Special components of cardiomyocytes - T-tubuls, gap junctions a SR

Ce infulx from the extracellular space is necessary fo initiation of the contraction, by the contraction requires much more ions

Excitation-contraction coupling - Ca release from SR

Calcium induced Ca release from SR

Contraction force is dependent on the concentration of Ca in SR

Excitation-contraction coupling - relaxation

Energy demanding process

Secondary active

transport

Effect of cardiac glykosides

Relationship between force and frequencyBowdich (Treppe) effect

Higher frequency

Intracellular Na

Shorter diastole

Less Ca expelled form

the cell

Effect of catecholamines

Ca channel phosphorylation

Faster contraction

Phospholamban

Faster relaxation

Thank you

for your

attention

Pictures and schemes – Berne, Levy - Physiology; 6th - Arronson, Ward - The CV System at a Glance

- Guyton, Hall - Textbook of Medical Physiology, 11th