32 R.G. Pertwee
Göthertetal.1999;MolderingsandGöthert1999;Pertwee2004a).Thereisevidence
that this putative receptor can be activated both by the cannabinoids—CP55940,
R-(+)-WIN55212 and anandamide—and by non-CB 1 , non-CB 2 ligands such as
aganodine and clonidine, and that this activation is sensitive to antagonism by
SR141716A (1 μM), LY320135 (0.1 or 1 μM) and rauwolscine (30 μM) (reviewed
in Pertwee 2004a). It also appears that this proposed receptor may belong to the
G protein-coupled receptor family originally known as endothelial differentiation
gene (EDG) receptors and that it can be activated by 1-oleoyl-lysophosphatidic
acid (Molderings et al. 2002).
Mang et al. (2001) have obtained evidence that anandamide can act on nerve ter-
minals of the myenteric plexus–longitudinal muscle preparation of the guinea-pig
ileum to inhibit electrically evoked release of the contractile transmitter acetyl-
choline through a mechanism that is independent of both TRPV1 and CB 1 recep-
tors. Thus, the inhibitory effects of anandamide on electrically evoked release of
[^3 H]acetylcholine and on electrically evoked contractions of this isolated tissue
preparation were insensitive to antagonism by 1 μM capsazepine. They were also
much less sensitive to antagonism by SR141716A than expected for CB 1 -mediated
effects. Results from other experiments with this tissue preparation suggest that
anandamide can increase both basal acetylcholine release from neurons and lon-
gitudinal muscle tone by acting on neuronal TRPV1 receptors (Mang et al. 2001).
Additional support for the presence of a non-CB 1 receptor for anandamide in the
gastro-intestinal tract comes from experiments both with the strips of longitudinal
muscle obtained from guinea-pig distal colon (Kojima et al. 2002) and with the
rat isolated gastric fundus (Storr et al. 2002). In the colon experiments, evidence
was obtained that anandamide, possibly after its conversion to active metabolites,
can induce contractions by acting through a TRPV1 and CB 1 receptor-independent
mechanism (Kojima et al. 2002). 2-Arachidonoyl glycerol also seems to act through
such a mechanism to induce contractions of this tissue preparation (Kojima et al.
2002). In the gastric fundus experiments it was found that at 10 μM, the CB 2 -
selective antagonist AM630 attenuated anandamide- but notR-(+)-WIN55212-
induced inhibition of electrically evoked contractions (Storr et al. 2002). It is
likely that anandamide was acting on prejunctional neurons in this tissue, as it
did not affect contractions produced by 5-HT or carbachol. AM630 has also been
found to antagonize∆^9 -THC, CP55940,R-(+)-WIN55212, methanandamide and
anandamide in the mouse isolated vas deferens in an agonist-dependent and com-
petitive manner. However, in this bioassay system, AM630 was less potent as an
antagonist of anandamide than ofR-(+)-WIN55212 (Pertwee et al. 1995). In view
of evidence that the mouse vas deferens expresses neuronal CB 2 -like receptors
that can mediate inhibition of electrically evoked contractions (Griffin et al. 1997;
Sect. 4.1.3), it may be that AM630 was producing its antagonism of cannabinoids
in this tissue by competing for these putative CB 2 -like receptors.