PUFA N-acylethanolamines increase intracellular calcium through cannabinoid and TRPV1 receptors

N. Alharthi, S. P. Alexander. School of Life Sciences, University of Nottingham, Nottingham, United Kingdom.

Background: Both CB₁ and CB₂ cannabinoid receptors are described to inhibit adenylyl cyclase and activate extracellular signal-regulated kinase, although only CB₁ receptors are described to regulate ion channel function¹. Anandamide (N-arachidonoylethanolamine) acts at both these receptors and also through activation of TRPV1 receptors, which are non-selective cation channels. In this study, we have compared polyunsaturated (PUFA) N-acylethanolamines (NAEs) for the ability to elevate intracellular calcium ions in cells expressing CB₁, CB₂ and TRPV1 receptors.

Methods: Intracellular calcium levels were monitored in CHO-hCB₁ and CHO-hCB₂ cells using a FlexStation, while rat dorsal root ganglion (DRG) neurones were used to assay TRPV1 in a calcium imaging apparatus². Data were collected from at least four separate preparations and were expressed relative to positive controls (ATP for CHO cells, and capsaicin for DRG cells).

Results: Anandamide evoked an elevation of intracellular calcium levels in CHO-hCB₁, CHO-hCB₂ and rat DRG neurones (Table). In CHO-hCB₂ cells, there appeared to be little variation in responses evoked by any of a series of polyunsaturated NAEs. For DRGs with endogenous TRPV1 receptors, there was also little variation in the level of responses, with the exception of N-eicosapentaenoylethanolamine, which appeared less effective. For CB₁ cannabinoid receptors, however, ω-6 NAEs appeared to evoke consistent responses, while responses to ω-3 NAEs were difficult to distinguish from baseline responses.

Conclusions: We conclude that there is heterogeneity of responses to polyunsaturated NAEs for CB₁ receptors in comparison to CB₂ and TRPV1 receptors, at least in terms of coupling to intracellular calcium ion levels.

References:

1. Pertwee et al. (2010). Pharmacol Rev PMID:21079038

2. Sagar et al. (2005). Eur J Neurosci PMID:16045490

Acknowledgement: We are grateful to the Saudi Cultural Bureau for financial support.