Bioelectromagnetics. 2002 Sep;23(6):475-9
Effects of Non Uniform Static Magnetic Fields on the Rate of Myosin Phosphorylation
Engstrom S, Markov MS, McLean MJ, Holcomb RR, Markov MM
INTRODUCTION
The MagnaBlocTM magnetic therapeutic device [Holcomb, 1994; Source: Amway Corporation, Ada, MI] is clinically successful in reducing various forms of pain: wrist pain, lower back pain [Holcomb et al., 1991], and arthritic knee pain [Segal et al., 2001].
The device consists of four NdFeB permanent magnets arranged with alternating polarities in a 2 2 array (Fig. 1). There is some understanding of the biological mechanisms at the cellular level from studies of action potential blockade [McLean et al., 1995], as well as cell swelling [McLean et al., 2000], but the physical mechanism underlying these observations remains elusive. Myosin phosphorylation as a tool to study biological effects initiated by magnetic fields was pioneered by Shuvalova et al. [1991].
The magnetic sensitivity of myosin phosphorylation has since been studied by one of us (M.S.M.) for 10 years, including work to establish optimal conditions for successful execution of the assay [Markov and Pilla, 1997]. The same fundamental process has been examined with focus on a wide range of parameters: static fields [Markov et al., 1993; Markov and Pilla, 1997], field shielding with high permeability materials [Markov et al., 1993], extremely low frequency magnetic fields [Markov et al., 1993; Markov and Pilla, 1994b], as well as chemical properties [Markov and Pilla, 1994a]. The canonical low field magnetic field experiment was recently the subject of an unsuccessful replication attempt [Coulton et al., 2000].
The present study marks a continuation of the use of this system for characterization of biological effects of magnetic fields, this time for relatively strong gradient fields. The biophysical interaction of the field has previously been modeled as a factor in the binding of calcium ions to calmodulin binding sites [Pilla et al., 1997], but it is not clear that this model carries over to the present exposure levels. It has been previously observed that the spatially inhomogeneous nature of the field surrounding the MagnaBloc device may be part of the physical metric responsible for biological effects seen at different locations in its magnetic field [Cavopol et al., 1995], and for this reason we contrast two lateral positions over the device in this investigation.
Another issue regarding the therapeutic usefulness of a magnetic device is its ability to penetrate tissue and produce a clinically beneficial field at a physiological target. Evidence using single cell action potentials suggests an effective distance threshold of 25 mm for the present device. Information from the present alternative biological assay is valuable in understanding the range in which one may expect biological effect of the device.
The myosin phosphorylation assay has two properties that makes it particularly well suited for studying the spatial characteristics of a gradient field: (1) the exposed volume is not very large (100 ml), providing a relatively localized field and gradient distributions; (2) the physical target ensemble is in solution and thus very likely isotropically distributed in space, allowing for some simplifying assumptions for the field description.
METHODS
The experiments described in this study were performed by using myosin light chains (MLC) and myosin light chain kinase (MLCK) isolated from turkey gizzard, kindly donated by M. Ikebe (University of Massachusetts, Amherst MA).
The reaction involves a basic solution composed of 40 mM HEPES buffer, pH 7.0, 0.5 mM magnesium acetate, 1 mg/ml bovine serum albumin, 0.1% (w/v) Tween 80, and 1 mM EGTA as well as 2.5 mM free Ca2•,70 nM scintillation counter (Model LS 6500, Beckman, Fullerton, CA) that counted 32P incorporated into myosin light chains.
For each position of the tube in the magnetic field, 5 or 11 independent runs of the experiment were conducted (Table 2). The internal repetition rate was 6 readings for each independent run.