Visualisation of Vascular Cannabinoid Receptors and their Potential Interaction with α1-adrenergic Receptors

Daly, C.J. , Wallace, G., White, K., Chris, H., Irving, A. and McGrath, J.C. (2008) Visualisation of Vascular Cannabinoid Receptors and their Potential Interaction with α1-adrenergic Receptors. Proceedings of the Physiological Society 13, King's College London, 2008.

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The role of cannabinoid receptors (CB1 & CB2) within the cardiovascular system is unclear. The endogenous cannabinoid anandamide (AEA) mediates vasodilation in vitro[1] whilst in vivo a triphasic blood pressure response comprising pressor and depressor components has been reported[2]. A possible role for CB1 and CB2 receptors exists within vascular tissue. However, non-CB mediated responses in the vasculature have been observed and a role for the orphan receptor GPR55 has been postulated[3]. The aims of this study were to a) investigate the role of endogenous cannabinoids in mouse tail artery, a thermoregulatory vessel rich in α1-adrenoceptors and b) examine, for the first time, the binding of a novel fluorescent ligand for CB receptors (Tocrifluor 1117). Tail arteries were removed from 4 month old male C57 black mice. Vessel segments were either mounted in a wire myograph for functional studies or incubated in Tocrifluor 1117 (0.5μM) & QAPB (1μM, fluorescent α1-adrenoceptor antagonist) for confocal analysis. Concentration response curves (CRC) to noradrenaline (NA) were performed in the presence and absence of the endocannabinoids AEA (1μM) and 2-arachidonylglycerol (2-AG, 1μM). Tocrifluor 1117 and QAPB were imaged under 488nm and 529nm excitation respectively. Tocrifluor 1117 binding was also examined in HEK293 cells stably expressing GPR55. AEA 1μM caused a transient contraction in isolated tail artery segments (0.08g). The NA CRC was shifted to left in the presence of 1μM AEA (Log EC50 control -6.80 vs -7.82, p<0.05). The maximum contractile response was unchanged. In the presence of 2-AG (1μM) a small leftward (non -significant) shift of the NA CRC was observed. However, comparison of the effect of 2-AG alone (Log EC50 -7.36) and 2-AG plus indomethacin (10μM , Log EC50 -6.33) revealed a significant difference (p>0.05). Tocrifluor 1117 binding was most evident on perivascular fat, adventital cells, nerves and smooth muscle. In several areas of media, colocalisation of Tocrifluor 1117 and QAPB was observed. In live HEK293 GPR55 cells, Tocrifluor 1117 generated a rise in Ca++ and promoted receptor clustering, visible as punctate fluorescence which developed over time. Tocrifluor 1117 (fluorescent analogue of the CB1 antagonist AM251) is a potentially very powerful tool for identifying the cellular location of cannabinoid receptors, including GPR55 in living tissues. AM251 has been shown to activate GPR55[4]. The results of the study suggest that endogenous cannabinoids potentiate the actions of noradrenaline in tail artery possibly via co-localised cannabinoid (GPR55?) and α1-adrenergic receptors in vascular smooth muscle. The importance of the CB/GPR55 receptors in perivascular fat and adventitia requires further study.

Item Type:Conference or Workshop Item
Additional Information:Poster Communication.
Glasgow Author(s) Enlighten ID:McGrath, Professor John and Daly, Professor Craig
Authors: Daly, C.J., Wallace, G., White, K., Chris, H., Irving, A., and McGrath, J.C.
College/School:College of Medical Veterinary and Life Sciences > School of Life Sciences

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