Uterine arteries were contracted with norepinephrine (NE, 3 μmol/L) and followed by additions of NS309. A. Normoxic animals. B. Normoxic pregnant animals in the absence (control) or presence of iberitoxin (IBTX, 100 nmol/L), charybdotoxin (CTX, 70 nmol/L), or apamin (500 nmol/L). C. High altitude hypoxic animals. Data are means ± SEM of tissues from 5–6 animals in each group.