Abstract

In vivo experiments have demonstrated (a) that transient electrical potentials are induced in impact-loaded bone, and (b) that bone formation is increased in response to electrical stimulation. Therefore, it has been hypothesized that, in response to mechanical loading, mechanical energy in bone is transduced into biologically relevant electrical energy. In order to study the mechanism through which electric fields may increase bone formation, a model system was developed were bone cells or bone organ cultures were exposed to a capacitively-coupled electric field of low frequency (8-25 Hz) and extremely low amplitude (estimated 10-7 V/cm in the culture medium) for 30 minutes.

Using this model system it was found that alkaline phosphatase rich (ie; more differentiated) calvarial cells exhibited a frequency-dependent increase in both release of mitogen activity into the culture medium and cell proliferation with a maximum effect occuring at 16 Hz. Furthermore, it was found that electric field-stimulated calvarial cell proliferation was dependent on acute release of mitogen activity into the culture medium. In addition, this acute electric field-stimulated release of mitogen activity was independent of de novo protein synthesis but could be blocked by a calmodulin antagonist.

The effect of electric field-exposure on bone organ cultures was also examined. Similiar to the effect on cell cultures, it was found that electric field exposure increased both the release of mitogen activity and bone cell proliferation in embryonic chick tibiae. Electric field exposure also increased bone matrix formation in these embryonic chick tiabiae. Interestingly, it was found that a 30 min/d exposure increased bone matrix formation to a greater extent than the increase from a constant exposure.

The following hypothesis was constructed to account for the observed effects of electric field-exposure on skeletal tissue. First, electric field-exposure stimulates the release of a pre-synthesized mitogen (possibly from plasma membrane-associated vesicles) from differentiated (ie; osteoblastic) bone cells in a Ca/calmodulin dependent manner. The mitogen(s) thus released then act on less differentiated bone cells to increase the rate of cell proliferation. This response was associated with increased phosphorylation of proteins and lipids in the target cells. The increase in cell proliferation results in an increase in bone cell number, which, in turn, results in increased bone matrix formation.

LLU Discipline

Biochemistry

Department

Biochemistry

School

Graduate School

First Advisor

John Randolph Farley

Second Advisor

William Ross Adey

Third Advisor

Kin-Hing William Lau

Fourth Advisor

Bruce Wilcox

Fifth Advisor

E. Clifford Hermann

Degree Name

Doctor of Philosophy (PhD)

Degree Level

Ph.D.

Year Degree Awarded

1998

Date (Title Page)

9-1998

Language

English

Library of Congress/MESH Subject Headings

Bone Development; Electromagnetics -- therapeutic use; Growth Substances

Type

Dissertation

Page Count

vii; 94

Digital Format

PDF

Digital Publisher

Loma Linda University Libraries

Usage Rights

This title appears here courtesy of the author, who has granted Loma Linda University a limited, non-exclusive right to make this publication available to the public. The author retains all other copyrights.

Collection

Loma Linda University Electronic Theses and Dissertations

Collection Website

http://scholarsrepository.llu.edu/etd/

Repository

Loma Linda University. Del E. Webb Memorial Library. University Archives

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