AHEART Mar. 45/3

Doughty, Joanne M., Frances Plane, and Philip D. Langton. Charybdotoxin and apamin block EDHF in rat mesenteric artery if selectively applied to the endothelium. Am. J. Physiol. 276 (Heart Circ. Physiol. 45): H1107–H1112, 1999.—In rat mesenteric artery, endothelium-derived hyperpolarizing factor (EDHF) is blocked by a combination of apamin and charybdotoxin (ChTX). The site of action of these toxins has not been established. We compared the effects of ChTX and apamin applied selectively to the endothelium and to the smooth muscle. In isometrically mounted arteries, ACh (0.01–10 μm), in the presence of indomethacin (2.8 μM) and Nv-nitro-L-arginine methyl ester (L-NAME) (100 μM), concentration dependently relaxed phenylephrine (PE)-stimulated tone (EC50 50 nM; n 5 10). Apamin (50 nM) and ChTX (50 nM) abolished this relaxation (n 5 5). In pressurized arteries, ACh (10 μM), applied intraluminally in the presence of indomethacin (2.8 μM) and L-NAME (100 μM), dilated both PEstimulated (0.3–0.5 μM; n 5 5) and myogenic tone (n 5 3). Apamin (50 nM ) and ChTX (50 nM) applied intraluminally abolished ACh-induced dilatations. Bath superperfusion of apamin and ChTX did not affect ACh-induced dilatations of either PE-stimulated (n 5 5) or myogenic tone (n 5 3). This is the first demonstration that ChTX and apamin act selectively on the endothelium to block EDHF-mediated relaxation.