Calcium/calmodulin‐dependent protein kinase II modulates inositol‐3‐phosphate receptors in vascular endothelium from mouse mesenteric arteries (1075.1)

Endothelial Ca 2+ pulsar consists in a spontaneous Ca 2+ release from IP 3 R localized within myoendothelial projections (MEP). We recently showed CaMKII activation by Ca 2+ pulsars, thus modulating endothelial function through NO production. Moreover, CaMKII is a known regulator of intracellular Ca 2+ homeostasis in several cell types. Our hypothesis was that Ca 2+ pulsar‐activated CaMKII modulates endothelial intracellular Ca 2+ dynamics. Our investigation showed that preincubation with KN‐93 (10 µM), CaMKII inhibitor, significantly altered endoplasmic reticulum (ER) Ca 2+ content (≍ ‐60%). A similar KN‐93‐induced alteration of ER Ca 2+ levels (≍ ‐55%) was observed while SERCA pumps were inhibited (Thapsigargin; 1 µM). However, inhibition of IP 3 R (2APB; 100 µM) precluded KN‐93 effect on ER Ca 2+ content. Colocalization (<40nm) of CaMKII and IP 3 R was observed by PLA in situ hybridization. In addition, an isoform‐specific distribution within MEP (IP 3 R2>IP 3 R1>IP 3 R3) has been found by in situ immunofluorescence. Finally, KN‐93 induced recruitment of new Ca 2+ pulsars sites (1.8‐Fold). These results suggest that CaMKII modulates intracellular Ca 2+ dynamics through modulation of IP 3 R activity. Thereby, CaMKII is involved in a negative feedback loop as an endothelial calcium‐sensor switch regulating Ca 2+ homeostasis. Grant Funding Source : Supported by FRQS, FICM, CFI, SQHA and HSFC