Stimulation of growth and calcium influx in cultured, bovine, aortic endothelial cells by platelets and vasoactive substances.

Endothelial cells (EC) line the heart and blood vessels, and they are the principal cellular components of the microvasculature. The presence of circulating platelets is believed to be necessary to maintain the integrity of the capillary endothelium. Growing EC in culture provides an opportunity to simulate the in vivo situation and to study the response of these cells to platelets and platelet secretions. The addition of platelets at a concentration of 10⁴-10⁵/mm³ and substances which circulate in blood following injury (serotonin, thrombin, ADP, epinephrine, norepinephrine and histamine) stimulate endothelial proliferation from 150–1,000% of controls. That substances so diverse in form have similar effects suggests a common mode of action, such as mobilization of a second messenger. The influx of ⁴⁵calcium (⁴⁵Ca⁺⁺) in response to these agents was found to be 5 to 24 times that of controls. The stimulation of ⁴⁵Ca⁺⁺ influx appears to be dose-dependent, and it is inhibited by pre-incubation with lanthanum chloride and specific blocking agents. Calcium as a second messenger is implicated in a variety of cellular functions including division, secretion, motility and enzyme regulation. Thus, the theorized supportive role of platelets on endothelium may be dual and operate, at least at the initial level, by a common mechanism: to mobilize calcium for stimulus-division following injury and for stimulus-secretion in normal metabolic activities.