Age‐related Changes in Endothelial Ca2+ Signaling Revealed by Imaging from Inside Arteries at Normal Physiological Pressures

Abstract

Aging is the summation of many, mostly invisible, but deleterious changes associated with altered structure and function of the cardiovascular system. Age‐induced impairment of endothelial function contributes to and reinforces the changes that occur in vascular disease. Normally, the endothelium transduces multiple chemical and mechanical signals into changes in cytoplasmic calcium (Ca2+) concentration that control vascular function. Thus, understanding age‐related functional changes in the endothelium requires an appreciation of Ca2+ control. We developed a wide‐field, gradient‐index (GRIN) fluorescence imaging system to visualize the endothelium from within the lumen of intact, pressurized arteries. The GRIN system enables rapid imaging of a 500 μm diameter area of the curved endothelial surface (~200 endothelial cells; ECs) with subcellular resolution. We also developed a semi‐automated data extraction procedure to quantify signal dynamics in the individual ECs loaded with fluorescent Ca2+ indicators. In the carotid artery of young rats (3 months), acetylcholine (ACh) evoked endothelial Ca2+ signals that were suppressed as intraluminal pressure increased. In aged rats (18 months) the pressure‐dependent suppression of ACh‐evoked Ca2+ signaling and the frequency of ACh‐evoked intracellular Ca2+ oscillations were reduced, whilst the temporal propagation of Ca2+ signals increased. Significantly, dose response measurements revealed that aging increased EC sensitivity to ACh, yet had no effect on the magnitude of the Ca2+ response in each cell. We propose that such alterations in EC Ca2+ signaling may manifest as a loss of functionality, and explain endothelial dysfunction in aging.