CB ₁ Receptor Antagonist SR141716A Inhibits Ca ²⁺ -Induced Relaxation in CB ₁ Receptor-Deficient Mice

Abstract

Abstract-Mesenteric branch arteries isolated from cannabinoid type 1 receptor knockout (CB 1 Ϫ/Ϫ ) mice, their wild-type littermates (CB 1 ϩ/ϩ mice), and C57BL/J wild-type mice were studied to test the hypothesis that murine arteries undergo high sensitivity Ca 2ϩ -induced relaxation that is CB 1 receptor dependent. Confocal microscope analysis of mesenteric branch arteries from wild-type mice showed the presence of Ca 2ϩ receptor-positive periadventitial nerves. Arterial segments of C57 control mice mounted on wire myographs contracted in response to 5 mol/L norepinephrine and responded to the cumulative addition of extracellular Ca 2ϩ with a concentration-dependent relaxation that reached a maximum of 72.0Ϯ6.3% of the prerelaxation tone and had an EC 50 for Ca 2ϩ of 2.90Ϯ0.54 mmol/L. The relaxation was antagonized by precontraction in buffer containing 100 mmol/L K ϩ and by pretreatment with 10 mmol/L tetraethylammonium. Arteries from CB 1 Ϫ/Ϫ and CB 1 ϩ/ϩ mice also relaxed in response to extracellular Ca 2ϩ with no differences being detected between the knockout and their littermate controls. SR141716A, a selective CB 1 antagonist, caused concentration-dependent inhibition of Ca 2ϩ -induced relaxation in both the knockout and wild-type strains (60% inhibition at 1 mol/L). O-1918, a cannabidiol analog, had a similar blocking effect in arteries of both wild-type and CB 1 Ϫ/Ϫ mice at 10 mol/L. In contrast, 1 mol/L SR144538, a cannabinoid type 2 receptor antagonist, or 50 mol/L 18␣-glycyrrhetinic acid, a gap junction blocker, were without effect. SR141716A (1 to 30 mol/L) was also assessed for nonspecific actions on whole-cell K ϩ currents in isolated vascular smooth muscle cells. SR141716A inhibited macroscopic K ϩ currents at concentrations higher than those required to inhibit Ca 2ϩ -induced relaxation, and appeared to have little effect on currents through large conductance Ca 2ϩ -activated K ϩ channels. These data indicate that arteries of the mouse relax in response to cumulative addition of extracellular Ca 2ϩ in a hyperpolarization-dependent manner and rule out a role for CB 1 or CB 2 receptors in this effect. The possible role of a nonclassical cannabinoid receptor is discussed. (Hypertension. 2002;39:251-257.) Key Words: mesenteric arteries Ⅲ calcium Ⅲ relaxation Ⅲ potassium channels O ver the past several years, a novel, extracellular Ca 2ϩ -activated, vasodilator pathway has been described in isolated rat arteries. The current model describing this system holds that elevation of extracellular Ca 2ϩ , as occurs in the interstitial compartments of some tissues, activates a Ca 2ϩ -sensing receptor localized on perivascular sensory nerves. Activation of this receptor causes the release of a transmitter that diffuses to underlying vascular smooth muscle and induces hyperpolarization-mediated relaxation through activation of a vascular smooth muscle cannabinoid type 1 (CB 1 ) receptor. 1 Among the findings that support this pathway are the demonstration that dorsal root ganglia and perivascular sensory nerv...

Anandamide initiates Ca2+ signaling via CB2 receptor linked to phospholipase C in calf pulmonary endothelial cells

“…On the other hand, in rat mesenteric arteries, anandamide has been found to initiate endothelial-dependent relaxation via an SR141716A-sensitive receptor that is distinct from CB1 . This conclusion is supported by reports of SR141716A-sensitive anandamide-and Ca 2 þ -induced relaxation in CB1 receptor knockout mice Bukoski et al, 2002). Overall, these results emphasize the existence of a non-CB1, but SR141716A-sensitive cannabinoid receptor on endothelial cells.…”

Nonpsychotropic Cannabinoid Receptors Regulate Microglial Cell Migration

“…To our knowledge, this is the first study to report that 2-AG is a full agonist at abn-CBD receptors. We ruled out the involvement of CB1 receptors in the 2-AG-triggered microglial cell migration because this response was not antagonized by 30 nM SR141716A, a concentration that antagonizes CB1 receptors (IC 50 ϭ 5 nM) without affecting abn-CBD receptors (IC 50 ϭ 600 nM) (Jung et al, 1997;Bukoski et al, 2002). Additionally, we show that THC and abnormalcannabidiol induce a synergistic increase in microglial cell migration.…”

Endocannabinoids Acting at Cannabinoid-1 Receptors Regulate Cardiovascular Function in Hypertension

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