RyR2 modulates a Ca2+-activated K+ current in mouse cardiac myocytes

Area of Science:

• Cardiovascular Physiology
• Ion Channel Function
• Cardiac Electrophysiology

Background:

• Voltage-dependent Ca2+ channels (VDCCs) trigger cardiac contraction via Ca2+ release from the sarcoplasmic reticulum (SR) through RyR2 channels.
• Small-conductance Ca2+-activated K+ channels (SK channels) are known to couple with VDCCs in cardiac muscle.
• The specific role of RyR2-mediated Ca2+ release in SK channel function within the heart remains largely unexplored.

Purpose of the Study:

• To investigate the involvement of RyR2-sensitive Ca2+ release in the activation and modulation of SK channels in cardiac myocytes.
• To elucidate the molecular mechanisms linking RyR2 and SK channels in the heart.

Main Methods:

• Whole-cell patch clamp electrophysiology was used to record Ca2+-activated K+ currents (IK,Ca) in isolated adult mouse atrial myocytes.
• Pharmacological agents like ryanodine and thapsigargin were employed to inhibit RyR2 and SERCA, respectively.
• RyR2 function was modulated using caffeine, and its expression was reduced via lentivirus-mediated shRNA (RyR2 knockdown).
• Co-immunoprecipitation assays were performed to detect protein complexes between SK2 and RyR2 in native cardiac tissue.
• Confocal imaging was used to assess intracellular Ca2+ ([Ca2+]i) levels.

Main Results:

• Inhibition of RyR2 with ryanodine significantly decreased IK,Ca, indicating RyR2's role in basal SK channel activity.
• Combined inhibition of RyR2 and SERCA further reduced IK,Ca, highlighting the importance of SR Ca2+ handling.
• Caffeine-induced activation of RyR2 led to a significant increase in IK,Ca.
• RyR2 knockdown resulted in decreased IK,Ca and intracellular Ca2+ fluorescence intensity.
• Co-immunoprecipitation confirmed a physical interaction between SK2 and RyR2 in native cardiac tissue.

Conclusions:

• RyR2-mediated Ca2+ release is essential for the activation and modulation of SK channels in cardiac myocytes.
• A direct molecular interaction exists between RyR2 and SK2 channels in the heart.
• These findings uncover a novel signaling pathway involving RyR2 and SK channels that regulates cardiac function.