Magnetic fields applied to collagen-coated ferric oxide beads induce stretch-activated calcium flux in human fibroblasts. Glogauer, M., J. Ferrier, C. A. G. McCulloch. MRC Group in Periodontal Physiology, and Department of Periodontics, Faculty of Dentistry, University of Toronto, Toronto, Ontario, CANADA
APStracts 2:0191C, 1995.
The ability to apply controlled forces to the cell membrane may enable elucidation of the mechanisms and pathways involved in signal transduction in response to applied physical stimuli. We have developed a magnetic particle-electromagnet model which allows the application of controlled forces to the plasma membrane of substrate attached fibroblasts. The system allows applied forces to be controlled by the magnitude of the magnetic field and by the surface area of cell membrane covered with collagen-coated ferric beads. Analysis by single cell ratio fluorimetry of fura-2 loaded cells demonstrated large calcium transients (50-300 nM) in response to the magnetic force applications. Experiments using either the stretch activated channel blocker gadolinium chloride, or EGTA to eliminate external calcium ions, or addition of extracellular manganese ions, indicated that there was a calcium influx through putative stretch activated channels. The probability of a calcium influx in single cells was increased by higher surface bead loading and reduced by the degree of cell spreading. Depolymerization of actin filaments by cytochalasin D increased the amplitude of calcium response two-fold. The regulation of calcium flux by filamentous actin content and by cell spreading indicates a possible modulatory role for the cytoskeleton in channel sensitivity. Magnetic force application to beads on single cells provides a controlled model to study mechanisms and heterogeneity in physical force stimulation of cation-permeable channels. 

Received 6 February 1995; accepted in final form 4 May 1995.
APS Manuscript Number C65-5.
Article publication pending Am. J. Physiol. (Cell Physiology).
ISSN 1080-4757 Copyright 1995 The American Physiological Society.
Published in APStracts on 16 May 1995.