Effect of low-frequency, low-amplitude magntic fields on the permeability of cationic liposomes entrapping carbonic anhydrase.I. Evidence for charged lipid involvement.

The influence of low frequency (4–16 Hz), low amplitude (25–75 μT) magnetic fields on the diffusion processes in enzyme-loaded unilamellar liposomes as bioreactors was studied. Cationic liposomes containing dipalmitoylphosphatidylcholine, cholesterol, and charged lipid stearylamine (SA) at different molar ratios (6:3:1 or 5:3:2) were used. Previous kinetic experiments showed a very low self-diffusion rate of the substrate p-nitrophenyl acetate (p-NPA) across intact liposome bilayer. After 60 min of exposure to 7 Hz sinusoidal (50 μT peak) and parallel static (50 μT) magnetic fields the enzyme activity, as a function of increased diffusion rate of p-NPA, rose from 17 ± 3% to 80 ± 9% (P < .0005, n = 15) in the 5:3:2 liposomes. This effect was dependent on the SA concentration in the liposomes. Only the presence of combined sinusoidal (AC) and static (DC) magnetic fields affected the p-NPA diffusion rates. No enzyme leakage was observed. Such studies suggest a plausible link between the action of extremely low frequency magnetic field on charged lipids and a change of membrane permeability.