Role of endothelial Ca2+ in LPS‐induced ICAM‐1 expression in lung microvessels

Abstract

In sepsis, ICAM‐1 expression is augmented in endothelial cells of lung microvessels. However, the role of endothelial cytosolic Ca2+ in the induction of ICAM‐1 expression is not known. Toward this, we blood‐perfused isolated rat lungs. We introduced a microcatheter through the left atrial cannula and then infused LPS (100μg/ml) into microvessels for 30 min. After 60 min, we determined ICAM‐1 expression by indirect in situ immunofluorescence. We recorded confocal images of surface microvessels using a LSM‐710 imaging system and quantified fluorescence intensity along the wall of microvessels. Intensity of ICAM‐1 expression was higher in LPS‐treated microvessels (venule 132.2±9.2; capillary 56.9±4.3, p< 0.001, n=3) compared to saline‐treated controls (12.6±1.8; 7.0±0.6 mean±SE, n=3). To establish the role of Ca2+, we infused Xestospongin‐C (25 μM), an inhibitor of inositol‐1,4,5‐trisphosphate (IP3) receptor on the endoplasmic reticulum (ER), into microvessels 10 min prior to LPS infusion. Xestospongin markedly reduced LPS‐induced lCAM‐1 expression in both microvessels (28.3±1.7; 8.2±0.4, n=2), indicating a role for IP3 in the process. We interpret from these data that LPS induction of ICAM‐1 expression in microvessels depends on IP3‐mediated ER Ca2+ release. Thus, we show for the first time that endothelial Ca2+ increase may be important in LPS‐induced responses in lung microvessels. (NIH HL75503)