The endogenous cannabinoid anandamide inhibits cromakalim-activated K+ currents in follicle-enclosed Xenopus oocytes.
The effect of the endogenous cannabinoid anandamide on K(+) 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 microM) reversibly inhibited cromakalim-induced K(+) currents, with an IC(50) value of 8.1 +/- 2 microM. Inhibition was noncompetitive and independent of membrane potential. Coapplication of anandamide with the cannabinoid type 1 (CB(1)) receptor antagonist N-(piperidin-1-yl)-5-(4-chlorophenyl)-1-(2,4-dichlorophenyl)-4-methyl-1H-pyrazole-3-carboximide hydrochloride (SR 141716A) (1 microM), the CB(2) receptor antagonist N-[(1S)endo-1,3,3-trimethyl bicyclo heptan-2-yl]-5-(4-chloro-3-methylphenyl)-1-(4-methylbenzyl)-pyrazole-3-carboxamide (SR144528) (1 microM), or pertussis toxin (5 microg/ml) did not alter the inhibitory effect of anandamide, suggesting that known cannabinoid receptors are not involved in anandamide inhibition of K(+) currents. Similarly, neither the amidohydrolase inhibitor phenylmethylsulfonyl fluoride (0.2 mM) nor the cyclooxygenase inhibitor indomethacin (5 microM) affected anandamide inhibition of K(+) 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 +/- 0.4 microM. Gonadotropin-induced oocyte maturation and the cromakalim-acceleration of progesterone-induced oocyte maturation were significantly inhibited in the presence of 10 microM anandamide. Collectively, these results indicate that cromakalim-activated K(+) 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.
Oz
Murat
M
National Institute on Drug Abuse/Intramural Research Program Integrative Neuroscience Section, 333 Cassell Dr., Baltimore, MD 21224, USA. moz@intra.nida.nih.gov
Yang
Keun-Hang
KH
Dinc
Meral
M
Shippenberg
Toni S
TS
D000818:Animals; D001095:Arachidonic Acids / Q000494:pharmacology*; D002118:Calcium / Q000378:metabolism; D001892:Camphanes / Q000494:pharmacology; D019806:Cromakalim / Q000037:antagonists & inhibitors*; D004533:Egtazic Acid / Q000031:analogs & derivatives / Q000494:pharmacology; D063388:Endocannabinoids; D005260:Female; D005905:Glyburide / Q000378:metabolism; D054086:KATP Channels / Q000187:drug effects*; D009865:Oocytes / Q000187:drug effects* / Q000378:metabolism; D037342:Pertussis Toxin / Q000494:pharmacology; D010880:Piperidines / Q000494:pharmacology; D053284:Polyunsaturated Alkamides / Q000494:pharmacology*; D026902:Potassium Channel Blockers / Q000494:pharmacology*; D011720:Pyrazoles / Q000494:pharmacology; D000077285:Rimonabant; D014982:Xenopus laevis
D001095:Arachidonic Acids; D001892:Camphanes; D063388:Endocannabinoids; D054086:KATP Channels; D010880:Piperidines; D053284:Polyunsaturated Alkamides; D026902:Potassium Channel Blockers; D011720:Pyrazoles; C110630:SR 144528; D019806:Cromakalim; D004533:Egtazic Acid; D037342:Pertussis Toxin; C025603:1,2-bis(2-aminophenoxy)ethane-N,N,N',N'-tetraacetic acid; D000077285:Rimonabant; D005905:Glyburide; D002118:Calcium; C078814:anandamide