FIG. 3.

1,25D stimulates ATP release in a dose-dependent manner and is selective for the hormone in static osteoblasts. (A) Values of ATP concentration (expressed in nM) measured in the extracellular bath 2 min after the addition of 1–100 nM 1,25D to SAOS-2 and ROS 17/2.8 cultures compared with controls obtained for the addition of medium and 0.01% ethanol (VEH). (B) Values of ATP concentration (expressed in nM) measured in the extracellular bath of ROS 17/2.8 cultures 2 min after treatment with the natural metabolite 25D (10 nM), the synthetic antagonist 1β,25D (10 nM) in combination with 10 nM 1,25D, and 10 nM 17β-estradiol (E) compared with ATP values obtained for a control for vehicle (0.01% ethanol). Medium was collected 2 min after the indicated treatments, and ATP concentration was measured in the bulk extracellular solution using an ATP-sensitive luciferin-luciferase reaction and normalized to the protein concentration of the samples. Data shown are mean values ± SE obtained from n = 6–48 independent experiments. *p < 0.05; **p < 0.01.