Chicken embryo fibroblasts (CEF) exposed to a sinusoidally varying magnetic field (SVMF) (100 Hz, 700 μT, for 24 h) showed a remarkable rise of segmental rotational relaxation rate of adenosine deaminase (ADA, EC 220.127.116.11) as determined by multifrequency phase fluorometry. Pyrene‐labeled, small subunit ADA was applied to cultured (normal) CEF, which have available and abundant ADA complexing protein (ADCP) on their plasma membranes. Sine‐wave‐modulated fluorometry of the pyrene yielded a profile of phase angle vs. modulation frequency. In SVMF‐treated cells and in Rous‐sarcoma‐virus (RSV) transformed cells the differential phase values at low modulation frequencies of the excitation are remarkably reduced. This effect is magnetic rather than thermal, because the temperature was carefully controlled and monitored; nevertheless to further check this matter we studied CEF, infected by the RSV‐Ts68 temperature‐sensitive mutant (36°C transformed, 41°C “revertant”). When grown at 36°C in the SVMF, cells did not show the slightest trend towards reversion, as would be expected had there been local heating. Concomitant with the increased segmental rotational relaxation rate of ADA, there was a decrease in fluorescence lifetime and a slight, yet significant, increase in membrane lipid “microfluidity.” These biophysical observations prompted us to examine the effect of SVMF on cell proliferation and ADA activity (a malignancy marker): higher rates of cell proliferation and reduced specific activity of ADA were observed. © 1993 Wiley‐Liss, Inc.
- membrane dynamics
- multifrequency differential phase fluorometry
- sine‐wave‐modulated fluorometry