The Endogenous Cannabinoid Anandamide Inhibits Cromakalim-Activated K⁺Currents in Follicle-EnclosedXenopusOocytes

Abstract

The effect of the endogenous cannabinoid anandamide on K ϩ currents activated by the ATP-sensitive potassium (K ATP ) channel opener cromakalim was investigated in follicle-enclosed Xenopus oocytes using the two-electrode voltage-clamp technique. Anandamide (1-90 M) reversibly inhibited cromakaliminduced K ϩ currents, with an IC 50 value of 8.1 Ϯ 2 M. Inhibition was noncompetitive and independent of membrane potential. Coapplication of anandamide with the cannabinoid type 1 (, or pertussis toxin (5 g/ml) did not alter the inhibitory effect of anandamide, suggesting that known cannabinoid receptors are not involved in anandamide inhibition of K ϩ currents. Similarly, neither the amidohydrolase inhibitor phenylmethylsulfonyl fluoride (0.2 mM) nor the cyclooxygenase inhibitor indomethacin (5 M) affected anandamide inhibition of K ϩ currents, suggesting that the effects of anandamide are not mediated by its metabolic products. In radioligand binding studies, anandamide inhibited the specific binding of the K ATP ligand [ 3 H]glibenclamide in the oocyte microsomal fractions, with an IC 50 value of 6.3 Ϯ 0.4 M. Gonadotropin-induced oocyte maturation and the cromakalim-acceleration of progesterone-induced oocyte maturation were significantly inhibited in the presence of 10 M anandamide. Collectively, these results indicate that cromakalim-activated K ϩ currents in follicular cells of Xenopus oocytes are modulated by anandamide via a cannabinoid receptor-independent mechanism and that the inhibition of these channels by anandamide alters the responsiveness of oocytes to gonadotropin and progesterone.

The Nonpsychoactive Cannabinoid Cannabidiol Inhibits 5-Hydroxytryptamine3A Receptor-Mediated Currents in Xenopus laevis Oocytes

“…Unlike THC, it is virtually inactive at both CB1 and CB2 receptors (Pertwee, 2009; for review, see Izzo et al, 2009). CB1 and CB2 receptors are not expressed in X. laevis oocytes (Hejazi et al, 2006;Oz et al, 2007). Therefore, it is unlikely that the effect of CBD on 5-HT 3 receptors is mediated by the activation of CB1 or CB2 receptors.…”

Anandamide inhibits transport-related oxygen consumption in the loop of Henle by activating CB1 receptors

“…In addition, WIN55212, the selective agonist of CB1 receptors, markedly decreased activity on voltage-gated Na channels in dorsal root (13) and trigeminal ganglion neurons of rats (8) and frog parathyroid cells (20). Moreover, in experiments performed in follicular cells of Xenopus oocytes anandamide blocks cromakalim-dependent K currents, altering the responses to gonadotropin or progesterone (23). Because anandamide has been found to be synthesized in the renal medulla (6), it is likely that anandamide could be an autacoid or paracrine factor.…”

“…In addition, it has been reported that anandamide potently inhibits amino-acid transporters in a Na-dependent manner in neural tissue (26). Also, in parathyroid and neuronal tissues anandamide blocks the Na (20) and K currents, controlling hormonal-derived responses (23).…”

Endocannabinoids and Their Pharmacological Actions

“…Potassium Channels 3.5.1 ATP-Sensitive Inward Rectifier K ATP Channels of the 2TM Domain Family Oz et al (2007) have obtained evidence from experiments with Xenopus oocytes that anandamide can act independently of CB 1 or CB 2 cannabinoid receptors as a non-competitive inhibitor of K ATP channels (IC 50 ¼ 8.1 μM) and that this endocannabinoid also inhibits […”