Calcium incorporation in cultured chondroblasts perturbed by an electromagnetic field

We tested the hypothesis that electric perturbation influences ⁴⁵Ca incorporation in extracellular matrix (ECM) of cartilage in vitro. Hypertrophic chondroblasts of tibial epiphyses (HC), sternum (SC), and skin fibroblasts (F) were cultured from chick embryos. HC, SC, and F cells were micromass seeded three times per week and maintained at 37.5°C with 5% CO₂ for two weeks. Cultures were randomly designated control (C) or exposed (E) to a pulsed electromagnetic field (PEMF). A time course experiment of calcium incorporation for all cultured groups showed that 24 h of exposure produced the largest biological response in chondroblasts. Calcium incorporation required supplemental phosphate. Autoradiography data indicated that the calcium incorporation into macromolecules largely occurred in the ECM. ⁴⁵Ca steady-state perturbation was enhanced by Streptomyces hyaluronidase (SH) but not by testicular hyaluronidase (TH). ⁴⁵Ca incorporation experiments tested the effects of phosphate, SH, TH, and PEMF alone and in various combinations on these cultures. Only PEMF or SH plus PEMF with phosphate enhanced ⁴⁵Ca incorporation. Other experiments examined the effect of rotenone or freeze-thawing on cells exposed to PEMF. PEMF plus freeze-thaw enhanced calcium incorporation in HC only. PEMF appeared to cause disruption of the ECM, enhancing the probability of matrix calcification.