Suppression of a differentiation response in MC-3T3-E1 osteoblast-like cells by sustained, low-level, 30 Hz magnetic-field exposure

Extremely low-frequency (ELF) magnetic fields have been reported to be capa ble of influencing both tissue remodeling and cell phenotypic expression in culture. However, whether the cells or tissues respond directly to the mag netic Bur or to the electric field induced by the time-changing magnetic fl ux remains a controversial topic. To address this question, we developed an osteoblast cell assay based on the activity of alkaline phosphatase, an en zyme whose activity is up-regulated during the differentiation of bone cell s. MC-3T3-E1 cells plated at a confluent density were allowed to proceed th rough the differentiation process for 3 days, after which they were exposed to a 30 Hz, 1.8-mT r.m.s. magnetic field inducing a spatially varying elec tric field with a maximum intensity of 0.9 mV/m r.m.s. In situ assays of al kaline phosphatase activity at 4, g, 16 and 64h demonstrated a progressive inhibition of enzyme activity, the pattern of which maps to the intensity o f the induced electric field (R-2 = 0.5, P < 0.001), We interpret these res ults to indicate that cells are capable of responding to ELF induced electr ic fields at intensities below 1 mV/m, and that the principal effect on cel ls is an inhibition of differentiation. (C) 2000 by Radiation Research Soci ety.