Electrolytic generation of oxygen partially explains electrical enhancement of tobramycin efficacy against Pseudomonas aeruginosa biofilm.

The role of electrolysis products, including protons, hydroxyl ions, reactive oxygen intermediates, oxygen, hydrogen, and heat, in mediating electrical enhancement of killing of Pseudomonas aeruginosa biofilms by tobramycin (the bioelectric effect) was investigated. The log reduction in biofilm viable cell numbers compared to the numbers for the untreated positive control effected by antibiotic increased from 2.88 in the absence of electric current to 5.58 in the presence of electric current. No enhancement of antibiotic efficacy was observed when the buffer composition was changed to simulate the reduced pH that prevails during electrolysis. Neither did stabilization of the pH during electrical treatment by increasing the buffer strength eliminate the bioelectric effect. The temperature increase measured in our experiments, less than 0.2 degree C, was far too small to account for the greatly enhanced antibiotic efficacy. The addition of sodium thiosulfate, an agent capable of rapidly neutralizing reactive oxygen intermediates, did not abolish electrical enhancement of killing. The bioelectric effect persisted when all of the ionic constituents of the medium except the two phosphate buffer components were omitted. This renders the possibility of electrochemical generation of an inhibitory ion, such as nitrite from nitrate, an unlikely explanation for electrical enhancement. The one plausible explanation for the bioelectric effect revealed by this study was the increased delivery of oxygen to the biofilm due to electrolysis. When gaseous oxygen was bubbled into the treatment chamber during exposure to tobramycin (without electric current), a 1.8-log enhancement of killing resulted. The enhancement of antibiotic killing by oxygen was not due simply to physical disturbances caused by sparging the gas because similar delivery of gaseous hydrogen caused no enhancement whatsoever.

Bacterial biofilms and the bioelectric effect.

Bacterial biofilms are acknowledged to be a major factor in problems of ineffective sterilization often encountered in clinics, hospitals, and industrial processes. There have been indications that the addition of a relatively small direct current electric field with the sterilant used to combat the biofilm greatly increases the efficacy of the sterilization process. The results of the experiments reported in this paper support the concept of the "bioelectric effect" as reported by J.W. Costerton, B. Ellis, K. Lam, F. Johnson, and A.E. Khoury (Antimicrob. Agents Chemother, 38:2803-2809, 1994). With a current of 1 mA flowing through the chamber containing the biofilm, an increase in the killing of the bacteria of about 8 log orders was observed at the end of 24 h (compared with the control with the same amount of antibacterial agent but no current). We also confirmed that the current alone does not affect the biofilm and that there appear to be optimum levels of both the current and the sterilant that are needed to obtain the maximum effect.

Power lines and the geomagnetic field.

The metric of prime interest in power line epidemiological studies has been AC magnetic intensity. To consider also possible geomagnetic involvement, the orientation of a long straight power line is examined relative to a uniform geomagnetic field (GMF) with dip angle alpha. An expression is derived for the component of the total GMF that is parallel, at an elevation beta, to the circuital magnetic field that surrounds the line. This component is a function of the angles alpha and beta, the total geomagnetic intensity BT, and the angle theta between the axis of the power line and magnetic north. Plotting these geomagnetic parameters for known leukemia residences allows one to test for possible ion cyclotron resonance or other GMF interactions. This approach, in principle, is an easy addition to existing or planned studies, because residential access is not required to obtain local values for alpha, beta, theta, and BT. We recommend including these parameters in the design of epidemiological studies examining power line fields and childhood leukemia.

Ion resonance electromagnetic field stimulation of fracture healing in rabbits with a fibular ostectomy.

Rabbits with a fibular ostectomy were exposed for 28 days to magnetic fields that satisfied the ion resonance conditions for calcium or magnesium. The rabbits were exposed to whole body treatment for 1/2 hour, 3 hours, or 24 hours per day. The fibulae from the experimental and control animals were removed surgically and were subjected to force-deflection testing to establish the stiffness of the healed fracture. The fibulae from the rabbits exposed to the ion resonance magnetic fields were found to be 55-299% (p < 0.01) more robust than the fibulae from the control animals.

Electromagnetic gating in ion channels.

There have been many attempts to develop a theoretical explanation of the phenomena of electromagnetic field interactions with biological systems. None of the reported efforts have been entirely successful in accounting for the observed experimental results, in particular with respect to the reports of interactions between extremely low frequency (ELF) magnetic fields and biological systems at ion cyclotron resonance frequencies. The approach used in this paper starts with the Lorentz force equation, but use is made of cylindrical co-ordinates and cylindrical boundary conditions in an attempt to more closely model the walls of an ion channel. The equations of motion of an ion that result from this approach suggest that the inside shape of the channel plus the ELF magnetic fields at specific frequencies and amplitudes could act as a gate to control the movement of the ion across the cell membrane.

Kinetics of channelized membrane ions in magnetic fields.

The cyclotron resonance model for channel ion transport in weak magnetic fields is extended to include damping losses. The conductivity tensor is obtained for different electric field configurations, including the circuital field E phi normal to the channel axis. The conductivity behavior close to the cyclotron resonance frequency omega c is compared to existing Ca2+-efflux data in the literature. A collision time of .023 s results from this comparison under the assumption that K+ ions are transiting in a 0.35 G field. We estimate a mean kinetic energy of 3.5 eV for this ion at resonance. This model leads to discrete modes of vibration (eigenfrequencies) in the ion-lattice interaction, such that omega n = n omega c. The presence of such harmonics is compatible with recent results by Blackman et al. [1985b] and McLeod et al. [1986] with the interesting exception that even modes do not appear in their observations, whereas the present model has no restriction on n. This harmonic formalism is also consistent with another reported phenomenon, that of quantized multiple conductances in single patch-clamped channels.

Nifedipine is an antagonist to cyclotron resonance enhancement of 45Ca incorporation in human lymphocytes.

The incorporation of 45Ca in mixed human lymphocytes was measured following one-hour exposures of the cells to combined steady and periodic magnetic fields designed to probe for cyclotron resonance response in calcium incorporation. Measurements were made as a function of magnetic field frequency, up to 30 Hz, and as a function of magnetic field amplitude, up to 1.5 x 10(-4) Trms. The amplitude measurements demonstrated that the relative 45Ca uptake at resonance follows different mechanisms of interaction above and below 0.2 x 10(-4) Trms. After adjusting the magnetic field configuration for maximum incorporation, we then determined the effects of the calcium influx blocker nifedipine on 45Ca incorporation, with and without simultaneous exposure to this specific magnetic field combination. The presence of nifedipine in both unexposed and exposed cell suspensions resulted in decreased 45Ca uptake, presumably through the slow inward calcium channels. Evidence was found suggesting that nifedipine acts antagonistically to the 45Ca cyclotron resonance tuning signal.

Calcium cyclotron resonance and diatom mobility.

The hypothesis that movement of biological ions may be predicted by cyclotron resonance theory applied to cell membranes is tested in these experiments. Diatoms (Amphora coffeaeformis) were chosen as the biosystem since they move or don't move, depending on how much calcium is transported across the membrane. The experiments demonstrate that a particular ion (calcium) is apparently moved across the cell membrane in response to the DC and AC values of magnetic flux densities (B) and the frequency derived from the cyclotron resonance theory. A clear resonance is shown and a rather sharp frequency response curve is demonstrated. The experiments also show a dose response as the AC value of the flux density is varied, and that odd harmonics of the basic cyclotron frequency are also effective.

Dynamic characteristics of membrane ions in multifield configurations of low-frequency electromagnetic radiation.

We seek to extend the recent suggestion that classical cyclotron resonance of biologically important ions is implicated in weak electromagnetic field-cell interactions. The motion of charged particles in a constant magnetic field and periodic electric field is examined under the simplifying assumption of no damping. Each of the nine terms of the relative dielectric tensor is found to have a dependence on functions that include the factor (omega 2 - omega 2B)-1, where omega B is the gyrofrequency. We also find a plasmalike decomposition of the electric field into oppositely rotating components that could conceivably act to drive oppositely charged ions in the same direction through helical membrane channels. For weak low-frequency magnetic fields, an additional feature arises, namely, periodic reinforcement of the resonance condition with intervals of the order of tens of msec for biological ions such as Li+, Na+, and K+.

Electromagnetic fields induced by Helmholtz aiding coils inside saline-filled boundaries.

The use of Helmholtz aiding coils to induce small electromagnetic (EM) fields in living tissue for both medical and research purposes has become quite common. While much progress has been made in showing that these induced EM signals can cause a variety of effects in tissues and individual cells, a satisfactory explanation of how the effects occur or how the EM signals couple to the tissue has not yet emerged. To address the latter problem adequately, it becomes necessary to know the spatial distribution of the induced fields inside a given set of boundaries. This paper examines the situation used for much in vitro research where a cylindrical culture dish is filled with a conducting solution and placed between the Helmholtz coils. Two cases are considered. The first assumes that the coils are above and below the culture dish (the planes of the coils are parallel with the top and bottom of the dish); the second assumes that the planes of the coils are parallel with the sides of the dish. A closed form solution is obtained for both cases, and it is shown that the induced EM field distribution is markedly different for the two cases.