Expression of Cannabinoid Type 1 Receptors in Human Odontoblast Cells

The aim of this study was to investigate the functional expression of cannabinoid type 1 (CB1) receptors in human odontoblasts (HODs) and the possible internal mechanism.

In the present study, we examined the molecular and functional expression of the CB1 receptors in cultured HOD-like cells and native HODs obtained from healthy wisdom teeth.

Immunohistochemistry and immunofluorescence revealed that CB1 receptors localize to native HODs and HOD-like cells, respectively. Both reverse-transcription polymerase chain reaction and Western blot analysis confirmed gene and protein expression of CB1 receptors. The ultrastructural distribution by immunoelectron microscopy also found that CB1 receptors labeled by colloidal gold particles distribute sparsely in the cytoplasm and odontoblastic processes. In functional assays, 2-arachidonyl glycerol, as an agonist of CB receptors, elicited the increase of intracellular fluorescence intensity that could be inhibited by a CB1-specific receptor antagonist rather than a selective CB2 receptor antagonist with fluo-3AM Ca²⁺ fluorescence. The source of the increase of intracellular fluorescence intensity elicited by CB1 receptors was from extracellular Ca²⁺ but not intracellular Ca²⁺ stores. The process of 2-arachidonyl glycerol activating CB1 receptors modulated transient receptor potential vanilloid 1-mediated Ca²⁺ entry via the cyclic adenosine monophosphate signaling pathway.

We conclude that HODs can express functional CB1 receptors that may play an important role in mediating the physiological function in tooth pulp.