Abstract: Described herein are methods and compositions for use in improving a vascular barrier of endothelial cells. The methods may include the use of barrier agonist compounds and improved techniques for culturing endothelial cells. The improved methods and compositions for culturing endothelial cells may include at least one or more of the following: an adenylyl cyclase activator; an activator of Sphingosine-1-phosphate (S1P) receptor internalization; a direct or indirect inducer of tight junction protein expression, and a direct or indirect inducer of adherens junction protein expression.