Abstract no.: 8 Endothelium‐dependent relaxation in atherosclerotic aorta segments of apolipoprotein E‐deficient (apoE‐/‐) mice

Abstract

The present study investigated whether lesion‐free aorta segments of young apoE‐/‐ mice, which will later show endothelial dysfunction when atherosclerotic lesions develop, display normal endothelial function in comparison with ‘wild‐type’ (wt) C57Bl/6J mice. Endothelial function was assessed by studying endothelium‐dependent relaxation to acetylcholine (ACh) and concomitant elevations of endothelial internal calcium (Ca2+i). Therefore, atherosclerosis‐prone aorta strips were mounted in a myograph with the endothelial side down and loaded with fura2‐AM (340/380 excitation emission ratio in relative units, RU) to measure Ca2+i simultaneously with isometric force. In 90% of WT females (n = 10), 31% of WT males (n = 13), 100% of apoE‐/‐ females (n = 14) and 82% of apoE‐/‐ males (n = 11), relaxation of precontracted (1 μM phenylephrine, PE) strips by ACh (2 × 10−6 M) was accompanied by a contemporary increase of Ca2+i. ACh‐induced Ca2+i increase was not different between WT and apoE‐/‐ mice, but was greater in females than in males (0.14 ± 0.03 RU vs. 0.04 ± 0.03 RU, P < 0.05). Dose‐response curves for ACh (10−9 to 3 × 10−6 M) revealed EC50‐values for ACh‐induced relaxations, which were significantly smaller in apoE‐/‐ than in wt (respectively 21 ± 7 nM vs. 61 ± 30 nM for females and 51 ± 22 vs. 82 ± 14 nM for males, P < 0.05), pointing to a higher sensitivity of apoE‐/‐ segments to ACh. Except for wt males, in which relaxation seemed to be uncoupled from endothelial Ca2+i mobilization, EC50 values of ACh for calcium increase were similar for the three other groups (116 ± 47, 124 ± 16 and 117 ± 7 nM, respectively). It is concluded that before development of atherosclerotic lesions, apoE‐/‐ mice are more efficient than wt mice in transducing an increase of internal calcium upon muscarinic receptor stimulation into a nitric‐oxide dependent vasodilator response.