Bovine adrenal zona fasciculata (AZF) cells express bTREK-1 K+ channels that set the resting membrane potential. Inhibition of these channels by adrenocorticotropic hormone (ACTH) is coupled to membrane depolarization and cortisol secretion. Curcumin, a phytochemical with medicinal properties extracted from the spice turmeric, was found to modulate both bTREK-1 K+ currents and cortisol secretion from AZF cells. In whole-cell patch clamp experiments, curcurmin inhibited bTREK-1 with an IC50 of 0.93 mu M by a mechanism that was voltage-independent. bTREK-1 inhibition by curcumin occurred through interaction with an external binding site and was independent of ATP hydrolysis. Curcumin produced a concentration-dependent increase in cortisol secretion that persisted for up to 24 h. At a maximally effective concentration of 50 mu M curcumin increased secretion as much as 10-fold. These results demonstrate that curcumin potently inhibits bTREK-1 K+ channels and stimulates cortisol secretion from bovine AZF cells. The inhibition of bTREK-1 by curcumin may be linked to cortisol secretion through membrane depolarization. Since TREK-1 is widely expressed in a variety of cells, it is likely that some of the biological actions of curcumin, including its therapeutic effects, may be mediated through inhibition of these K+ channels. (c) 2008 Elsevier Inc. All rights reserved.