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 BK Ca channels. Furthermore, rotundifolone inhibited the vasoconstriction induced by CaCl 2 in depolarizing nominally Ca 2+-free medium and antagonized the contractions elicited by an L-type Ca 2+ channel agonist, S(-)-Bay K 8644 (2 · 10 )7 M), indicating that the vasodilatation involved inhibition of Ca 2+ influx through L-type voltage-dependent calcium channels (Ca v type-L). Additionally, rotundifolone inhibited L-type Ca 2+ currents (I Ca L), affecting the voltage-dependent activation of I Ca L 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 BK Ca channels and causes a shift in the steady-state inactivation relationship for Ca v type-L towards more hyperpolarized membrane potentials.Terpenoids constitute the largest class of plant secondary metabolites and have been used in essential oils for centuries as therapeutically relevant compounds. However, little is known about their mechanism of action [1,2].The monoterpenoids, such as camphor, borneol, citronellol, alpha-terpineol or menthol, compose a group of naturally occurring organic compounds derived from two isoprene units. They are the major components of some essential oils presenting anaesthetic and analgesic activities [3,4] Rotundifolone (C 10 H 14 O 2 ; molecular weight 166) is a naturally occurring monoterpenic ketone of plant origin and an important chemical constituent of the essential oils of many Mentha species (Mentha rotundifolia, M. suaveolens, M. spicata L., M. longifolia and M. x villosa) [19,20]. A previous report from our group showed that rotundifolone induced marked hypotension and bradycardia in non-anaesthetized normotensive rats using an in vivo approach. Those effects were probably due to a decrease in peripheral vascular resistance [21], a hypothesis that was subsequently str...

In vivo effect of essential oil of Mentha x villosa and its active compound against Schistosoma mansoni (Sambon, 1907)

“…Regarding ROT some effects reported in the literature, analgesic (Almeida et al, 1996), relaxant (Sousa et al, 2007), hypotensive and bradycardic (Guedes et al, 2002), antinociceptive (Sousa et al, 2007(Sousa et al, , 2009, antimicrobial (Arruda et al, 2006) and spasmolytic (Sousa et al, 2008). Studies have also demonstrated a possible mechanism of action involved in the relaxing effect exhibited by ROT (Silva et al, 2011).…”

Potassium Channel Activation Is Involved in the Cardiovascular Effects Induced by Freeze DriedSyzygium jambolanum(Lam.) DC Fruit Juice

“…For this we used Tyrode's solution modified with 20 mM KCl, a concentration sufficient to partially prevent efflux of K + and attenuate vasorelaxation mediated by the opening of K + channels [16, 17]. Additionally, we also experimented using TEA, a blocker of K + channels, at different concentrations (1, 3, and 5 mM) [27–29]. In all these situations, the effect of JSJ was significantly attenuated, and, for the differing TEA concentrations, the effect was concentration-dependent.…”

Involvement of Potassium Channels in Vasorelaxant Effect Induced byValeriana prionophyllaStandl. in Rat Mesenteric Artery

“…Rats were euthanized, and superior mesenteric artery was removed, cleaned from connective tissue and fat as described by Silva and colleagues [10]. Whenever appropriate, the endothelium was removed by gently rubbing the intimal surface of the vessels.…”

“…To investigate the involvement of K + channels, in the first set of experiments, vasorelaxation with VPR was performed in vessels with denuded endothelium that were precontracted with Phe in Tyrode's solution with elevated K + (20 mM equimolar replacement of NaCl with KCl) to attenuate K + efflux [10]. Additionally, in the second group of experiments, endothelium-denuded rings were incubated for 30 min with putative K + channel blockers before the second application of Phe (1  μ M), and the inhibition was calculated by comparing the response elicited by VPR, before and after the addition of the inhibitors.…”