[Effect of pulsed electromagnetic fields (PEMF) on osteoblast-like cells. Alterations of intracellular Ca2+].

Low-energy electromagnetic fields pulsed at frequencies of 60-90 Hz significantly increase healing of chronic fracture nonunions in man. These fields are effective at tissue current levels as low as several orders of magnitude lower than those required for transmembrane depolarization of normal cells. In this study, the effects of PEMF on culture of rat osteoblast-like cells have been examined. The PEMF promoted the growth of these cells, were also found to increase the basal level of [Ca2+]i, and to decrease the responses towards epidermal growth factor (EGF) and serum, when the degree of response was based on the intracellular Ca2+ transient. These effects of PEMF were mimicked by 12-O-tetradecanoyl phorbol 13-acetate (TPA), a potent activator of protein kinase C. Pretreatment of TPA enhanced the cell growth and suppressed the intracellular Ca2+ transient induced with EGF and then serum to about 170% of the control. Then, present study investigated how the PEMF and TPA modulate EGF receptors of these cells. Both PEMF and TPA decreased the level of EGF binding to these cells down to about 65% and 75%, respectively. Scatchard analysis revealed the decrease of EGF receptor without a significant change in the affinity for EGF by both. In conclusion, it was indicated that PEMF acts at cell membrane and modulates the receptors which is essential for cell growth and DNA synthesis.