IP3R‐dependent modulation of endothelial Ca2+ dynamics by CaMKII in mouse mesenteric arteries

Abstract

Local calcium dynamics such as Ca2+ pulsars appear to have a significant impact on endothelial function. These Ca2+ pulsars result from the spontaneous release of Ca2+ by IP3 receptors (IP3R) localized within the myoendothelial junction (MJ). We have recently shown that CaMKII, a Ca2+‐dependent kinase decoding Ca2+ oscillations, is activated by Ca2+ pulsars. However, CaMKII also regulates intracellular Ca2+ homeostasis in other cell types. CaMKII regulation of endothelial intracellular Ca2+ dynamics in native endothelium was then undertaken by confocal microscopy. Exposure to KN‐93, a CaMKII inhibitor, stimulated Ca2+ pulsar. In the absence of extracellular Ca2+, exposure to ionomycin provoked an increase in intracellular Ca2+, indicative of the endoplasmic reticulum (ER) content in Ca2+. Interestingly, preincubation with KN‐93 significantly impaired the ER Ca2+ content (−62%). However, SERCA inhibition by thapsigargin did not significantly alter the ionomycin‐induced Ca2+ increase in the presence of KN‐93. These results suggest that CaMKII regulates endothelial Ca2+ through the modulation of IP3R activity. Immunohistochemistry revealed a progressive intrusion of the different isoforms (IP3R2>;IP3R1>;IP3R3) within the MJ. Therefore, this study suggests that endothelial CaMKII inhibits Ca2+ pulsars through IP3R1/2 phosphorylation. Supported by FRQS, FICM, CFI and HSFC.