© 1998 American Heart Association, Inc.
Editorial |
Microtubules in Cardiac Hypertrophy
A Mechanical Role in Decompensation?
Correspondence to Henk E.D.J. ter Keurs, MD, PhD, FRCPC, Department of Medicine, Health Sciences Centre, University of Calgary, 3300 Hospital Drive, NW, Calgary AB T2N 4N1, Canada. E-mail Henk@cvr.ucalgary.ca
Key Words: heart failure • myocardial contraction • cytoskeleton • microtubule
Cardiac function
relies on the ability of the myocytes to develop force and shorten, as
well as on the geometry of the heart, which translates shortening into
stroke volume and force per cell into pressure in the lumen of the
chambers. The requirements of circulation are met by adjustment of
heart rate and power output by the myocytes. The heart adapts acutely
to a hemodynamic load by increasing myocyte force
output in response to stretch due to filling at elevated
end-diastolic pressure. The acute response of the
contractile system underlying Starling's law of the heart is followed
more gradually, but still remarkably rapidly,1 by
growth of the myocytes. Whereas stretch causes longitudinal growth by
apposition of sarcomeres in series, increased systolic stress
generated by the myocytes induces growth of myofibrils with a larger
cross-sectional area and, consequently, cells with a larger diameter
are produced. The latter response provides a feedback mechanism that
keeps systolic force of individual cross-bridges constant.
Within limits, these responses allow stable adaptation of cardiac
function to the hemodynamic requirements of the body.
When the requirements of circulation are still not met, the syndrome of
heart failure becomes manifest when short-term control systems have to
be activated constantly to maintain pump function that equals
(nearly) the circulatory demands. In the process of growth, cells
express novel protein isoforms with a character that depends on a host
of stimuli2 so the myocyte phenotype
alters substantially during development of hypertrophy and
progression to heart failure.3 The effect of
growth
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