Effect of low frequency, low amplitude magnetic fields on the permeability of cationic liposomes entrapping carbonic anhydrase II. No evidence for surface enzyme involvement

Observations recently reported by our group indicate that combined 7 Hz sinusoidal (B-acpeak = 50 mu T) and parallel static (B-dc = 50 mu T) magnetic fields can induce a significant increase in diffusion rate of substrate across carbonic anhydrase (CA)-loaded liposomes (DPPC:Chol:SA). A direct involvement of charges of stearylamine (SA) on the lipid membrane surface was also demonstrated. Kinetic studies showed that CA. was mainly entrapped in Liposomes at 5:3:2 molar ratio, although a small amount (17%) of enzyme was also located on the external surface of these cationic liposomes. In this paper we report steady state kinetic studies on this latter CA after ELF-EMFs exposure. No difference in the apparent K-m between exposed and sham samples was observed. On the contrary the apparent V-max was increased by approximately a factor of 2 after field exposure. In spite of the proteolytic digestion of this external CA, a significant increase of enzymatic activity, as a function of increase in the diffusion rate of substrate across the lipid bilayer, was observed in the exposed samples. Based on these results, a conformational change induced by the field on the CA located on the external surface of 5:3:2 liposomes is excluded as an explanation for our previous observations, supporting the primary role of bilayer SA in the interaction with ELF A model of ELF interaction, based on the Larmor precession theory, explaining the physical phenomenon induced on the dipole of SA has been developed. (C) 2000 Wiley-Liss, Inc