CANNABINOID CB1 RECEPTOR AND ENDOTHELIUM-DEPENDENT HYPERPOLARIZATION IN GUINEA-PIG CAROTID, RAT MESENTERIC AND PORCINE CORONARY-ARTERIES

1 The purpose of these experiments was to determine whether of not the endothelium-dependent hyperpolarizations of the vascular smooth muscl e cells (observed in the presence of inhibitors of nitric oxide syntha se and cyclo-oxygenase) can be attributed to the production of an endo genous cannabinoid. 2 Membrane potential was recorded in the guinea-pi g carotid, rat mesenteric and porcine coronary arteries by intracellul ar microelectrodes. 3 In the rat mesenteric artery, the cannabinoid re ceptor antagonist, SR 141716 (1 mu M), did not modify either the resti ng membrane potential of smooth muscle cells or the endothelium-depend ent hyperpolarization induced by acetylcholine (1 mu M) (17.3+/-1.8 mV , n=4 and 17.8+/-2.6 mV, n=4, in control and presence of SR 141716. re spectively). Anandamide (30 mu M) induced a hyperpolarization of the s mooth muscle cells (12.6+/-1.4 mV, n=13 and 2.0+/-3.0 mV. n=6 in vesse ls with and without endothelium, respectively) which could not be repe ated in the same tissue, whereas acetylcholine was still able to hyper polarize the preparation. The hyperpolarization induced by anandamide was not significantly influenced by SR 141716 (1 mu M). HU-210 (30 mu M), a synthetic CB1 receptor agonist, and palmitoylethanolamide (30 mu M), a CB2 receptor agonist, did not influence the membrane potential of the vascular smooth muscle cells. 4 In the rat mesenteric artery, t he endothelium-dependent hyperpolarization induced by acetylcholine (1 mu M) (19.0+/-1.7 mV, n=6) was not altered by glibenclamide (1 mu M: 17.7+/-2.3 mV, n=3). However, the combination of charybdotoxin (0.1 mu M) plus apamin (0.5 mu M) abolished the acetylcholine-induced hyperpo larization and under these conditions, acetylcholine evoked a depolari zation (7.7+/-2.7 mV, n=3). The hyperpolarization induced by anandamid e (30 mu M) (12.6+/-1.4 mV, n=13) was significantly inhibited by glibe nclamide (4.0+/-0.4 mV, n=4) but not significantly affected by the com bination of charybdotoxin plus apamin (17.3+/-2.3 mV, n=4). 5 In the g uinea-pig carotid artery, acetylcholine (1 mu M) evoked endothelium-de pendent hyperpolarization (18.8+/-0.7 mV, n=15). SR 141716 (10 nM to 1 0 mu M), caused a direct, concentration-dependent hyperpolarization (u p to 10 mV at 10 mu M) and a significant inhibition of the acetylcholi ne-induced hyperpolarization. Anandamide (0.1 to 3 mu M) did not influ ence the membrane potential. At a concentration of 30 mu M, the cannab inoid agonist induced a non-reproducible hyperpolarization (5.6+/-1.3 mV, n=10) with a slow onset, SR 141716 (1 mu M) did not affect the hyp erpolarization induced by 30 mu M anandamide (5.3+/-1.5 mV, n=3). 6 In the porcine coronary artery, anandamide up to 30 mu M did not hyperpo larize or relax the smooth muscle cells. The endothelium-dependent hyp erpolarization and relaxation induced by bradykinin were not influence d by SR 141716 (1 mu M). 7 These results indicate that the endothelium -dependent hyperpolarizations, observed in the guinea-pig carotid, rat mesenteric and porcine coronary arteries, are not related to the acti vation of cannabinoid CB1 receptors.