Selected Contribution: Time course and heterogeneity of contractile responses in
cultured human airway smooth muscle cells.
Fabry, Ben, Geoffrey N. Maksym, Stephanie A. Shore, Paul E. Moore, Reynold A.
Panettieri, Jr., James P. Butler, Jeffrey J. Fredberg.
1Physiology Program, Harvard School of Public Health, Boston, Massachusetts
02115; 2School of Biomedical Engineering, Dalhousie University, Halifax, Nova Scotia,
Canada B3H 3J5; and 3Pulmonary and Critical Care Division, University of
Pennsylvania School of Medicine, Philadelphia, Pennsylvania 19104
APStracts 8:0255A, 2001.
We measured the time course and heterogeneity of responses to contractile and relaxing
agonists in individual human airway smooth muscle (HASM) cells in culture. To this
end, we developed a microrheometer based on magnetic twisting cytometry adapted with
a novel optical detection system. Ferromagnetic beads (4.5 µm) coated with Arg-Gly-Asp
peptide were bound to integrins on the cell surface. The beads were twisted in a
sinusoidally varying magnetic field at 0.75 Hz. Oscillatory bead displacements were
recorded using a phase-synchronized video camera. The storage modulus (cell stiffness;
G'), loss modulus (friction; G«dprime»), and hysteresivity (?; ratio of G«dprime» to G')
could be determined with a time resolution of 1.3 s. Within 5 s after addition of histamine
(100 µM), G' increased by 2.2-fold, G«dprime» increased by 3.0-fold, and ? increased
transiently from 0.27 to 0.34. By 20 s, ? decreased to 0.25, whereas G' and G«dprime»
remained above baseline. Comparable results were obtained with bradykinin (1 µM).
These changes in G', G«dprime», and ? measured in cells were similar to but smaller than
those reported for intact muscle strips. When we ablated baseline tone by adding the
relaxing agonist dibutyryl cAMP (1 mM), G' decreased within 5 min by 3.3-fold. With
relaxing and contracting agonists, G' could be manipulated through a contractile range of
7.3-fold. Cell populations exhibited a log-normal distribution of baseline stiffness
(geometric SD = 2.8) and a heterogeneous response to both contractile and relaxing
agonists, partly attributable to variability of baseline tone between cells. The total
contractile range of the cells (from maximally relaxed to maximally stimulated),
however, was independent of baseline stiffness. We conclude that HASM cells in culture
exhibit a clear, although heterogeneous, response to contractile and relaxing agonists and
express the essential mechanical features characteristic of the contractile response
observed at the tissue level.
Received 9 February 2001; accepted in final form 19 April 2001
APS Manuscript Number A143-1.
Article publication pending J Appl Physiol
ISSN 1080-4757 Copyright 2001 The American Physiological Society.
Published in APStracts on 18 June 2001