In vascular smooth muscle cells, large-conductance Ca²⁺-activated K⁺ channels (K_Ca channels) play a pivotal role in determining membrane potential, and thereby the vascular tone. Ginsenoside Re, a phytochemical from ginseng, is reported to activate this channel, but its precise mechanism is unsolved. Patch clamp studies showed that ginsenoside Re activates K_Ca channels in the arterial smooth muscle cell line A10 in a dose-dependent manner. The channel-opening effect of ginsenoside Re was inhibited by 1 µM L-NIO, an inhibitor of eNOS, but not by 3 µM SMTC, an inhibitor of nNOS, indicating that ginsenoside Re activated K_Ca channels through activation of eNOS. SH-6 (10 µM), an Akt inhibitor, and wortmannin, a PI3-kinase inhibitor, completely blocked activation of K_Ca channels by ginsenoside Re, indicating that it activates eNOS via a c-Src/PI3-kinase/Akt-dependent mechanism. In addition, the ginsenoside Re-induced activation of eNOS and K_Ca channel was blocked by 10 µM ICI 182, 780, an inhibitor of membrane estrogen receptor-α, suggesting that eNOS activation occurs via a non-genomic pathway of this receptor. In conclusion, ginsenoside Re releases NO via a membrane sex steroid receptors, resulting in K_Ca channel activation in vascular smooth muscle cells, promoting vasodilation and preventing severe arterial contraction. J. Med. Invest. 54: 381-384, August, 2007