Osteoblastic cells were isolated and GJIC was evaluated as described in Materials and Methods. (A) Recombinant PTH(1-34) dose-dependently increased the degree of GJIC in osteoblastic cells isolated from young, but not mature or old, rats. (B) Recombinant PTH(1-34) (10−11–10−7 M) had no effect on Gja1 mRNA expression in osteoblastic cells from young, mature, or old rats. (C) Recombinant PTH(1-34) (10−11–10−7 M) had no effect on Cx43 protein expression in osteoblastic cells from young, mature, or old rats.. a indicates p < 0.05 compared to osteoblastic cells from mature rats; b indicates p < 0.05 versus osteoblastic cells from old rats; c indicates p < 0.05 young treated versus control. n=2-4 animals per age group per treatment.