Brain Microvasculature: Evidence for Interactive Endothelium-Dependent Responses Induced by Endothelin-1 and Nitric Oxide*

Previous in vivo and in vitro studies demonstrated a functional interaction between endothelin-1 (ET-1) and nitric oxide (NO) at the level of ETA receptors. The present experiments were designed to examine the involvement of the signal transduction pathway in ET-1 and NO modulation of Ca2+ mobilization and cytoskeletal filament organization. The results indicate that ET-1-stimulated Ca2+ mobilization was inhibited by NO in endothelial cells (ECs) derived from human brain microvessels or capillaries. This effect by NO was mimicked by 8-bromo cyclic guanosine monophosphate (cGMP) and was prevented by an inhibitor of guanylyl cyclase, ODQ, and an inhibitor of protein kinase G, Rp-8-pCPT-cGMP. NO and 8-bromo-cGMP modulation of Ca2+ mobilization were similarly affected by agents known to regulate other signals downstream of ET-1 stimulation. These findings demonstrate the close relation between NO and ET-1 in ECs. This interaction takes place at the level of the ET-1 receptor and downstream messenger pathway, leading to rapid changes in intracellular Ca2+. Therefore, ECs have the capacity to regulate endothelium-dependent responses involved in maintaining capillary tone, microcirculation, and blood-brain barrier function.