Rotundifolone-Induced Relaxation is Mediated by BKCa Channel Activation and Cav Channel Inactivation

Abstract:  Rotundifolone is the major constituent of the essential oil of Mentha x villosa Hudson. In preliminary studies, rotundifolone induced significant hypotensive, bradycardic and vasorelaxant effects in rats. Thus, to gain more insight into the pharmacology of rotundifolone, the aim of this study was to characterize the molecular mechanism of action involved in relaxation produced by rotundifolone. The relaxant effect was investigated in rat superior mesenteric arteries by using isometric tension measurements and whole-cell patch-clamp techniques. Rotundifolone relaxed phenylephrine-induced contractions in a concentration-dependent manner. Pre-treatment with KCl (20 mM), charybdotoxin (10−7 M) or tetraethylammonium (TEA 10−3 or 3 × 10−3 M) significantly attenuated the relaxation effect induced by rotundifolone. Additionally, whole-cell patch-clamp recordings were made in mesenteric smooth muscle cells and showed that rotundifolone significantly increased K+ currents, and this effect was abolished by TEA (10−3 M), suggesting the participation of BKCa channels. Furthermore, rotundifolone inhibited the vasoconstriction induced by CaCl2 in depolarizing nominally Ca2+-free medium and antagonized the contractions elicited by an L-type Ca2+ channel agonist, S(-)-Bay K 8644 (2 × 10−7 M), indicating that the vasodilatation involved inhibition of Ca2+ influx through L-type voltage-dependent calcium channels (Cav type-L). Additionally, rotundifolone inhibited L-type Ca2+ currents (ICaL), affecting the voltage-dependent activation of ICaL and steady-state inactivation. Our findings suggest that rotundifolone induces vasodilatation through two distinct but complementary mechanisms that clearly depend on the concentration range used. Rotundifolone elicits an increase in the current density of BKCa channels and causes a shift in the steady-state inactivation relationship for Cav type-L towards more hyperpolarized membrane potentials.