Abstract
Endothelial cells are reported to be glycolytic and to minimally rely on mitochondria for ATP generation. Rather than providing energy, mitochondria in endothelial cells may act as signaling organelles that control cytosolic Ca(2+) signaling or modify reactive oxygen species (ROS). To control Ca(2+) signaling, these organelles are often observed close to influx and release sites and may be tethered near Ca(2+) transporters. In this study, we used high-resolution, wide-field fluorescence imaging to investigate the regulation of Ca(2+) signaling by mitochondria in large numbers of endothelial cells (∼50 per field) in intact arteries from rats. We observed that mitochondria were mostly spherical or short-rod structures and were distributed widely throughout the cytoplasm. The density of these organelles did not increase near contact sites with smooth muscle cells. However, local inositol trisphosphate (IP(3))-mediated Ca(2+) signaling predominated near these contact sites and required polarized mitochondria. Of note, mitochondrial control of Ca(2+) signals occurred even when mitochondria were far from Ca(2+) release sites. Indeed, the endothelial mitochondria were mobile and moved throughout the cytoplasm. Mitochondrial control of Ca(2+) signaling was mediated by ATP production, which, when reduced by mitochondrial depolarization or ATP synthase inhibition, eliminated local IP(3)-mediated Ca(2+) release events. ROS buffering did not significantly alter local Ca(2+) release events. These results highlight the importance of mitochondrial ATP production in providing long-range control of endothelial signaling via IP(3)-evoked local Ca(2+) release in intact endothelium.