Ca²⁺-dependent nitric oxide release in endothelial but not R3230Ac rat mammary adenocarcinoma cells

We have characterized the ability of several cell types associated with the microvasculature of solid tumors to release nitric oxide (NO·) in response to increases in cytosolic Ca2+ concentration ([Ca2+](c)). EA.hy926 immortalized human umbilical vein endothelial cells (EC) rat fibroblasts (RFL), and tumorigenic cells isolated from R3230Ae rat mammary adenocarcinoma (MaC) were treated with thapsigargin (TG), an inhibitor of Ca2+-ATPase. NO· output was measured via a chemiluminescence detection system. Baseline NO· output was detectable only for EC. TG caused a significant increase in EC NO· output that could be blocked with N(G)- monomethyl-L-arginine and restored with L-arginine. TG did not stimulate NO· release from RFL or MaC cells, despite elevating [Ca2+](c) in all cells. A Ca2+-dependent isoform of NO synthase (eNOS) was detected by immunoblot only in EC. These data indicate that EC, but not RFL or MaC, are capable of Ca2+-dependent NO· release and suggest that any Ca2+-dependent NO· release within this tumor is primarily of endothelial (and not tumorigenic cell) origin.

Duke Scholars

Author Mark Wesley Dewhirst Radiation Oncology