Ca(2+) handling in isolated human atrial myocardium

Area of Science:

• Cardiology
• Physiology
• Molecular Biology

Background:

• Human atrial and ventricular myocardium share identical beating rates but may differ in contractile behavior.
• Intracellular calcium (Ca2+) handling in human atrium under physiological conditions is not well understood.

Purpose of the Study:

• To investigate and compare intracellular Ca2+ handling and contractile behavior in human atrial and ventricular myocardium.
• To elucidate the mechanisms underlying the force-frequency relationship and rest-interval effects in both cardiac chambers.

Main Methods:

• Utilized rapid cooling contractures (RCCs) to measure sarcoplasmic reticulum (SR) Ca2+ content.
• Employed the photoprotein aequorin to assess intracellular Ca2+ transients.
• Studied atrial and ventricular muscle strips isolated from nonfailing human hearts.

Main Results:

• Both atrial and ventricular myocardium demonstrated a positive force-frequency relation, with increased SR Ca2+ turnover.
• Atrial myocardium showed decreased postrest twitch force and RCCs with longer rest intervals, unlike ventricular myocardium.
• Rest intervals in atria may lead to SR Ca2+ loss (leak) and subsequent Ca2+ extrusion via Na+/Ca2+ exchange.

Conclusions:

• The positive force-frequency relation in human atria and ventricles is driven by enhanced SR Ca2+ turnover.
• Atrial contractility and Ca2+ handling are depressed after rest periods, suggesting rest-dependent SR Ca2+ leak.
• Rate and rhythm influence mechanical performance differently in atrial and ventricular myocardium.