An endothelial cell that lines the interior surface of the afferent arteriole and maintains vascular tone. This cell responds to changing ion concentrations and blood pressure by releasing vasoactive substances, in order to regulate blood flow into the glomeruli, which is essential for glomerular filtration. [ http://www.ncbi.nlm.nih.gov/pubmed/24066938 http://www.ncbi.nlm.nih.gov/pubmed/25834230 http://www.ncbi.nlm.nih.gov/pubmed/16990493 http://www.ncbi.nlm.nih.gov/pubmed/22733355 ]