SERUM PLAYS A CRITICAL ROLE IN MODULATING [CA2-CELLS EXPOSED TO WEAK ION-RESONANCE MAGNETIC-FIELDS(](C) OF PRIMARY CULTURE BONE)

Primary-culture bone cells were exposed to ion-resonance (IR) magnetic fields tuned to Ca2+. Cytosolic calcium concentration, [Ca2+](c), was measured by using fura-2 during field exposure. The fields investigat ed were 20 mu T static + 40 mu T p-p at either 15.3 or 76.6 Hz, and 0. 13 mT static + either 0.5 or 1.0 mT p-p at 100 Hz. Other parameters in cluded field orientation, culture age (2 or 5 days after plating), and the presence of serum (0 or 2%) during exposure. Total experiment tim e was 29.5 min: The field was applied after 2 min, and bradykinin was added as an agonist control after 22 min. The data were quantified on a single-cell basis during the 2-22 min exposure period in terms of th e magnitude of the largest occurring [Ca2+](c) spike normalized to loc al baseline. Field-exposed and control groups were characterized in te rms of the percent of cells exhibiting spike magnitudes above threshol ds of 100 or 66% over baseline and were compared by using Fisher's exa ct test. Without serum, there was little evidence that IR magnetic fie lds altered [Ca2+](c). However, in the presence of 2% serum, 3 of the 16 experiments exhibited significant effects at the 100% threshold. Re ducing this threshoId to 66% resulted in five experiments exhibiting s ignificant effects. Most strikingly, in all of these cases, the field acted to enhance [Ca2+](c) activity as opposed to suppressing [Ca2+](c ) activity. These findings suggest a role for serum or for constituent s within serum in mediating the effects of IR magnetic fields on cells and may provide a resolution pathway to the dilemma imposed by theore tical arguments regarding the possibility of such phenomena. Possible roles of serum and future studies are discussed. (C) 1997 Wiley-Liss, Inc.