Ca(2+) current facilitation is CaMKII-dependent and has arrhythmogenic consequences

Area of Science:

• Cardiology
• Molecular and Cellular Electrophysiology
• Calcium Channel Regulation

Background:

• Cardiac voltage-gated Ca(2+) current (ICa) is essential for heart function, influencing electrophysiology, excitation-contraction coupling, and cellular energetics.
• Numerous pathways regulate cardiac ICa, highlighting its complex role in myocardial activity.

Purpose of the Study:

• To review the dynamic changes in cardiac ICa during the action potential.
• To elucidate the roles of Ca(2+)-dependent inactivation (CDI) and Ca(2+)-dependent facilitation (CDF) in ICa regulation.
• To detail the involvement of calmodulin (CaM) and CaMKII in modulating ICa.

Main Methods:

• Review of existing literature on cardiac calcium channel regulation.
• Analysis of mechanisms underlying Ca(2+)-dependent inactivation (CDI) and facilitation (CDF).
• Examination of the roles of CaM and CaMKII in L-type Ca(2+) channel function.

Main Results:

• CDI, mediated by CaM binding to the L-type Ca(2+) channel C-terminus, provides negative feedback on Ca(2+) influx, especially at high myocyte Ca(2+) loads.
• CDF, dependent on CaMKII phosphorylation, enhances peak ICa over successive beats, leading to a staircase effect and slower inactivation.
• CDI and CDF act concurrently to fine-tune the ICa waveform, with CDF potentially counteracting inactivation at higher heart rates and contributing to arrhythmias.

Conclusions:

• CDI and CDF are critical, co-existing mechanisms that dynamically regulate cardiac ICa during the action potential.
• Calmodulin and CaMKII are key molecular players in mediating these inactivation and facilitation processes.
• Understanding these regulatory pathways is vital for comprehending cardiac electrophysiology and potential arrhythmia mechanisms.