Proof of eNOS-type NOS in a transgenic mouse model. (A) RBCs in blood samples from WT mice exhibited positive staining for eNOS. (B) Negative staining of RBCs was observed in blood samples derived from eNOS^-/- mice (n = 3). l-arginine-induced changes in accumulated nitrite concentration in blood confirm the activity of (C) RBC-NOS in WT mice but not in (D) eNOS^-/- mice. ^*Significant difference from control. #Significant difference from l-NNA.