CaMKII regulates intracellular Ca²⁺ dynamics in native endothelial cells

Area of Science:

• Cardiovascular Physiology
• Cellular Signaling
• Endothelial Biology

Background:

• Endothelial Ca2+ signaling, including Ca2+ pulsars, influences vascular smooth muscle contraction.
• Ca2+ pulsars involve IP3R-dependent Ca2+ release and Ca2+-dependent kinase (CaMKII) activation.
• CaMKII activation can occur independently of extracellular Ca2+ influx.

Purpose of the Study:

• To investigate the reciprocal relationship between CaMKII and endothelial Ca2+ dynamics.
• To elucidate the role of CaMKII in regulating Ca2+ pulsars in mesenteric arteries.
• To understand the mechanistic impact of CaMKII on endoplasmic reticulum (ER) Ca2+ stores and IP3 receptor function.

Main Methods:

• Utilized high-speed confocal microscopy for intracellular Ca2+ monitoring.
• Employed CaMKII inhibition with KN-93 to assess effects on Ca2+ pulsars.
• Assessed ER Ca2+ content using ionomycin and measured IP3 receptor (IP3R) interactions via proximity ligation assays.

Main Results:

• CaMKII inhibition significantly increased Ca2+ pulsar activity (+89%).
• CaMKII inhibition accelerated ER Ca2+ emptying and reduced ER Ca2+ content (-61%) by relieving inhibition of IP3Rs.
• CaMKII interacts with IP3Rs, suggesting a direct regulatory mechanism.

Conclusions:

• CaMKII acts as a critical regulator of endothelial Ca2+ pulsars in native endothelium.
• CaMKII functions as a Ca2+-sensitive switch in a negative feedback loop controlling endothelial Ca2+ homeostasis.
• Isoform-specific localization of IP3Rs within myoendothelial projections (MEPs) was observed.