Bone Abstracts

We studied changes in intracellular Ca²⁺ concentration in bone cell cultures obtained from human subjects with osteoporosis and osteoarthritis, to evaluate differences between these patients and healthy subjects. We enrolled 36 patients: 12 undergoing primary total hip arthroplasty for osteoporotic femoral fractures (group A, mean age range 57–80), 12 for hip osteoarthritis (group B, mean age range 57–80), and 12 healthy subjects who suffered a high-energy trauma fracture (group C, mean age range 18–30) as controls. All patients gave informed consent for using bone samples as a source of bone cells. Lumbar spine and femoral DXA were perfomed. Microfluorimetric techniques of the intracellular calcium concentration was done by fura-2. Imaging was performed with the Argus 50 system (Hamamatsu) with excitation wavelengths of 340 and 380 nm for acquiring ratio images of fura-2. ATP and thapsigargin, inhibitor of the calcium-ATPase of the endoplasmic reticulum, were added during the experiments.Group A reported BMD value of 0.673±0.196 g/cm², group B 1.005±0.194 g/cm², and group C 1.179±0.259 g/cm². Application of ATP (1 mM) induced in group C, a fast and transient increase (ratio value from 0.67±0.01 to 1.74±0.13) in intracellular calcium concentration [Ca²⁺]_i. Addition of thapsigargin (100 nM) to the cells induced an additional increase of [Ca²⁺]_i (ratio value 0.85±0.03) due to release from intracellular calcium stores. In osteoblastic cultures (B) ATP significantly increased [Ca²⁺]_i (ratio value from 0.67±0.01 to 1.53±0.19) but in lower amount than control cells. In this experimental group thapsigargin induced a [Ca²⁺]_i increase (ratio value 0.98±0.05) slightly stronger than the control. In group A, ATP stimulation exhibited a significantly lower increase in [Ca²⁺]_I (ratio value from 0.67±0.01 to 1.21±0.09), while the effect of thapsigargin was similar to control (ratio value 0.87±0.06). Osteoporotic cultures indicate an impairment of intracellular calcium influx. P2 receptors may be important drug targets for bone turnover modulation.