Objectives: The location of odontoblasts (OBs) in the outermost pulp and the long process extending into the dentinal tubules make them well suited as sensors for detecting external stimuli. We have reported that symmetric dye- and electrical- coupling network widely exists between human OBs. Young OBs secreting dentin matrix are morphologically well known to have large gap-junctions. The aim of this study was to compare the conductivity through the couplings and electrical capacitance of cell clusters in different age groups. Methods: Core pulps were removed from 7 human premolars (13y, n=3; 16y, n=2; 21y, n=2) immediately after extraction. OBs were left behind on the dentin wall. Whole-cell dual patch-clamp method was used to monitor input membrane conductance and decay time-constant of the coupled- or clustered-cells. Results: Conductivity between coupled cell pairs in 13y- (16 pairs) and 15y-old-groups (13 pairs) was significantly higher than that in 21y-old-group (12 pairs) (One-way ANOVA, p<0.001). Transient current responses to a voltage step indicated that the time constant of the current decay was elevated as the number of OBs increased in every group. Significantly larger electrical capacitance was obtained from the clusters in 13y- (7 clusters) and 15-old-groups (5 clusters) than from those in 21y-old-group (4 clusters) (p<0.01). Conclusions: The present results indicated that the junctional system between OBs is more extensive in immature teeth, which may contribute to secretion signaling and protective roles against external irritation. We hypothesize that immature OBs, which function as a syncitium via the couplings rather than individually, need high conductance to neighboring cells corresponding to high potential of calcification. The decrease in electrical capacitance of OB clusters in mature teeth may deteriorate the functions. 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).

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