Cannabinoid CB1 receptor of cat cerebral arterial muscle functions to inhibit L-type Ca²⁺ channel current

Abstract

The CB1 subtype of the cannabinoid receptor is present on neurons in the brain and mediates the perceptual effects of Δ9-tetrahydrocannabinol and other cannabinoids. We found that cat cerebral arterial smooth muscle cells (VSMC) contain the protein for the CB1 receptor and express a cDNA that has >98% amino acid homology to the CB1 cDNA expressed in rat and human neurons. Activation of the CB1 cannabinoid receptor has been shown to decrease the opening of N-type voltage-gated Ca2+ channels in neurons through a pertussis toxin-sensitive GTP-binding protein. In the present study we tested the hypothesis that activation of the cannabinoid CB1 receptor in cerebral VSMC inhibits voltage-gated Ca2+ channels and results in cerebral vasodilation. The predominant Ca2+ current identified in cat cerebral VSMC is a voltage-gated, dihydropyridine-sensitive, L-type Ca2+ current. The cannabimimetic drug WIN-55,212-2 (10–100 nM) induced concentration-dependent inhibition of peak L-type Ca2+ current, which reached a maximum of 82 ± 4% at 100 nM ( n = 14). This effect was mimicked by the putative endogenous CB1-receptor agonist anandamide, which produced a concentration-related reduction of peak L-type Ca2+ current with a maximum inhibition (at 300 nM) of 39 ± 4% ( n = 12). The inhibitory effects of both ligands on peak L-type Ca2+currents were abolished by pertussis toxin pretreatment and application of the CB1-receptor antagonist SR-141716A (100 nM, n = 5). Both WIN-55,212-2 and anandamide produced concentration-dependent relaxation of preconstricted cerebral arterial segments that was abolished by SR-141716A. These results indicate that the CB1 receptor is expressed in cat cerebral VSMC and that the cerebral vasculature is one of the targets for endogenous cannabinoids. These findings suggest that the CB1 receptor and its endogenous ligand may play a fundamental role in the regulation of cerebral arterial tone and reactivity by modulating the influx of Ca2+ through L-type Ca2+ channels.

L-type channel inhibition by CB1 cannabinoid receptors is mediated by PTX-sensitive G proteins and cAMP/PKA in GT1-7 hypothalamic neurons

“…Inhibition of LTCCs by WIN 55,212-2 has been reported also in identified retinal bipolar cells [20] and in cerebral vascular smooth muscle cells [21]. In the latter case, WIN 55,212-2 and the endocannabinoid anandamide inhibited the LTCCs in a voltage-independent manner and the effects were PTX-sensitive.…”

Blood pressure regulation by endocannabinoids and their receptors

“…The in vivo cardiovascular effects of cannabinoids are complex and may comprise direct effects on the myocardium (Bonz et al, 2003) and vasculature (Gebremedhin et al, 1999;Járai et al, 1999;Wagner et al, 2001b), as well as modulation of autonomic outflow in the central (Niederhoffer and Szabo, 2000) and the peripheral nervous systems (Ishac et al, 1996;Malinowska et al, 1997). CB 1 receptors are present in the myocardium where they mediate negative inotropy (Bonz et al, 2003;Pacher et al, 2004) and also in the vasculature (Gebremedhin et al, 1999;Liu et al, 2000), where they lead to vasodilation (Gebremedhin et al, 1999), and both of these sites are implicated in the hypotensive effect of anandamide (Wagner et al, 2001b;Pacher et al, 2004).…”

“…CB 1 receptors are present in the myocardium where they mediate negative inotropy (Bonz et al, 2003;Pacher et al, 2004) and also in the vasculature (Gebremedhin et al, 1999;Liu et al, 2000), where they lead to vasodilation (Gebremedhin et al, 1999), and both of these sites are implicated in the hypotensive effect of anandamide (Wagner et al, 2001b;Pacher et al, 2004). The cardiovascular depressor effects of anandamide are devoid of a centrally mediated component , although some synthetic cannabinoids can cause centrally mediated sympathoexcitatory effects (Niederhoffer and Szabo, 2000).…”

“…To date, two such receptors have been identified: the CB 1 receptor, which is highly expressed in the brain (Matsuda et al, 1990), but is also present in heart and vascular tissues (Gebremedhin et al, 1999;Liu et al, 2000;Bonz et al, 2003), and the CB 2 receptor, expressed primarily by haematopoietic and immune cells (Munro et al, 1993). Arachidonoyl ethanolamide or anandamide and 2-arachidonoylglycerol, the natural ligands of these receptors, are lipid-like substances called endocannabinoids (reviewed by Mechoulam et al, 1998;Kunos et al, 2000).…”

Mechanisms of anandamide‐induced vasorelaxation in rat isolated coronary arteries

“…The endogenous cannabinoid, arachidonyl ethanolamide (anandamide) is a potent vasorelaxant in many isolated blood vessel types, including mesenteric (Randall et al, 1996;White & Hiley, 1997), cerebral (Ellis et al, 1995;Gebremedhin et al, 1999), renal (Deutsch et al, 1997) and coronary (Pratt et al, 1998) arteries. Whilst the cardiovascular actions of cannabinoids in anaesthetized whole animals are largely mediated by CB 1 receptors (Lake et al, 1997;Ja rai et al, 1999), there have been relatively few studies reporting cannabinoid relaxation of isolated blood vessels through cannabinoid CB 1 receptors (Gebremedhin et al, 1999); indeed, there is evidence that CB 1 receptors may be present on vascular smooth muscle but not stimulate vasorelaxation (Holland et al, 1999).…”