Localization of Intercellular Coupling between Collateral Processes of Human Odontoblasts

Objectives: Odontoblasts (OBs) are well-known to be associated with dentinogenesis, mainly triggered by dentin stimulation. They have a monopolar processus in the dentinal tubule and align in the outermost pulp. Thus, they seem suitable to be a possible sensor even though clear evidence for a role of OBs as sensory receptor cells has not been fully clarified. On the other hand, complicated branching network of dentinal tubules has been histologically shown. In this study, we tried to determine whether intercellular communication exists through branches of OB processes in the collateral dentinal tubules. Methods: Eight freshly extracted human premolars for orthodontic reasons from informed patients (15-22 yr) were used. Freshly isolated OBs (I-OBs) with a monopolar processus (>110 µm) were obtained from 4 teeth and plated in HEPE-based buffer. Transverse dentin discs were sectioned in the remaining 4 teeth. OBs (D-OBs) in the discs were also used. The existence of intercellular junctions through OB branches in dentin were examined by electron microscopy or electrophysiologically by dual-cell patch-clamp method. Results: (1) Symmetric intercellular conductance was obtained from cell pairs of both I-OBs (n=27) and D-OBs (n=29). (2) Coupling probability (I-OBs: 27/35, D-OBs: 29/35) and number of electrical couplings (I-OBs: 1.28 ± 0.25, I-OBs: 1.28 ± 0.25) were not significantly different between I-OBs and D-OBs. (3) Cell-to-cell contact between processes were observed rather than gap-junctional communications in collateral dentinal tubules. Conclusions: At least after maturation, no clear evidence was found to support gap-junctional communications between neighboring OBs through OB-branches. This study was supported by a Grant-in-Aid for Scientific Research from the Japanese Ministry of Education, Culture, Sports, Science and Technology.