AIM:To investigate mediating and regulatory effects of osteoblastic gap juncti onal intercellular communication(GJIC) on low-dose parathyroid hormones(PTH)-s timulated bone formation activities in vitro.METHODS:Rat calvarial osteoblasts ( ROBs) in cultures were divided into three groups according to the different mode of exposure.Group A: vehicle (sodium acetate, SA)-treated group; Group B:1×10-8 mol/L hPTH(1-34) intermittent exposure group;Group C:1×10-8 mol/L hPTH(1-34) +1×10-7mol/L TPA exposure group.48 h incubation cycles in three groups were repeated for eight times.GJIC and mineralized bone nodules formation in thr ee groups were detected using Lucifer Yellow (LY) scrape loading dye transfer (S LDT) and mineralized nodule staining together with nodule index,respectively. RE SULTS:At various measuring time points of SA×6 h in group A,PTH×6 h in group B ,PTH×6 h+1 h in group B and PTH×6 h+TPA×1 h in group C,LY(+) cell numbers were 6.8±2.5,19.5±6.5,14.0±3.6 and 5.7±2.4,respectively.Diffusion and transf er of LY fluorescent probe was much more noticeably discerned in group B than in group A and C(P< 0.01).Mineralized bone nodule indices were 45.2±12.5, 88.0±1 5.3 and 38.5±17.9 in group A,B and C respectively.Bone formation activity was m uch better revealed in group B than in group A and C (P< 0.01),whereas no statis tically significant difference of bone formation activities were found in group A compared with group C(P=0.465).CONCLUSION:Mediations and regulations of the co ordinating signals in osteoblastic network via GJIC essentially contribute to PT H-stimulated bone anabolism.However,disruption of GJIC not only hinders osteobl astic intercellular coordination but also frustrates PTH-induced bone formation activities in vitro.Therefore,GJIC may evidently play important roles in regula tions on low-dose PTH-induced bone formation. AIM: To studying mediating and regulatory effects of osteoblastic gap juncti onal intercellular communication (GJIC) on low-dose parathyroid hormones (PTH) -s timulated bone formation activities in vitro. METHODS: Rat calvarial osteoblasts (ROBs) in cultures were divided into three Groups B: 1 × 10-8 mol / L hPTH (1-34) intermittent exposure group; Group C: 1 × 10 -8 mol / L hPTH (1-34) + 1 × 10-7 mol / L TPA exposure group.48 h incubation cycles in three groups were repeated for eight times. GJIC and mineralized bone nodules formation in thr ee groups were detected using Lucifer RE SULTS: At various measuring time points of SA × 6 h in group A, PTH × 6 h in group B, PTH × (LY) scrape loading dye transfer (S LDT) and mineralized nodule staining together with nodule index, respectively. 6 h + 1 h in group B and PTH × 6 h + TPA × 1 h in group C, LY (+) cell numbers were 6.8 ± 2.5, 19.5 ± 6.5, 14.0 ± 3.6 and 5.7 ± 2.4, r espectively. Diffusion and transf er of LY fluorescent probe was much more noticeably discerned in group B than in group A and C (P <0.01) .Mineralized bone nodule indices were 45.2 ± 12.5, 88.0 ± 1 5.3 and 38.5 ± 17.9 in group A , B and C respectively. Bone formation activity was m uch better revealed in group B than in group A and C (P <0.01), with no statis tically significant difference of bone formation activities were found in group A compared with group C (P = 0.465) .CONCLUSION: Mediations and regulations of the co-ordinating signals in osteoblastic network via GJI essentially contribute to PT H-stimulated bone anabolism. Despite, disruption of GJIC not only hinders osteoblasticotic intercellular coordination but also frustrates PTH-induced bone formation activities in vitro.Therefore, GJIC may evidently play important roles in regula tions on low-dose PTH-induced bone formation.