Direct Cell-to-cell Network in Human Odontoblasts in the Tooth Disk

Objectives: We have used an experimental model of freshly isolated odontoblasts (OBs) to determine the possibility of OBs as sensors and shown cell-to-cell coupling network exists between human OBs and is affected by aging and extracellular pH. We have newly designed an odontoblast-dentin disk model, where OB processus are left in the dentinal tubules to reduce the possible damage of electrical and dye coupling during cell isolation. We tried to clarify to what extent human OBs have the coupling network in the disk. Methods: Three premolars were extracted from human volunteers (15, 16 and 20y) for orthodontic treatment. Teeth were sawed in the diagonal direction immediately after extraction. Core pulps were removed with of fine tweezers. Trypsin was used to remove cellular or fibrous fragments and to expose unbroken OB membrane. Electrophysiological recording was made from OBs using dual patch-clamp or intracellular configuration. We monitored input membrane conductance and decay time-constant of the OBs. Dye coupling was confirmed using Lucifer Yellow injected though an intracellular electrode into OBs iontophoretically. Results: Electrical potentials could be recorded from OBs considerably far from the injection site, sometimes on the nearly opposite side of the disk, in response to a current injection despite attenuation. Injected Lucifer Yellow was transported to OBs from the injection site and sometimes even to those on the other side. Electrical coupling probability between two OBs was the bigger near the pulp horn (43/49) than at the lateral wall of the pulp chamber (20/39) (Fisher's exact test, p<0.001). Conclusions: We have reconfirmed that human OBs function as a syncitium via the couplings rather than individually. The cell network extended to the opposite side in the diagonal section. This study was supported by a Grant-in-Aid for Scientific Research from the Japanese Ministry of Education, Culture, Sports, Science and Technology (No. 17390506).