Physiology of the Heart Daniel Hodyc Department 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 myocardiumVentricular 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 frequency Bowdich (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