Hi. I don't know about immortalized endothelial cells, but I grow endothelial cells I isolate from lung and aorta on plates coated with 0.1% Gelatin. I add about 4mL of 0.1% Gelatin (in PBS) solution to a 10cm plate, incubate at 37C or Room Temperature for at least an hour before plating.
Thank you Mrs. Ortiz. It seems like most coating reagents could be used. I was not sure whether they could be toxic etc. But now everything is more clear.
I have been using Angelica's method for about 10 years with great satisfaction. Another matrix to use is collagen. Please consult the article below for a detailed protocol how to use type 1 collagen for endothelial cell cultures.
Article Establishment of outgrowth endothelial cells from peripheral blood