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-adrenergic response in
cardiac hypertrophy
1 Department of Kinesiology and
Applied Physiology,
The role of microtubules in modulating
cardiomyocyte
-adrenergic response was investigated in rats with
cardiac hypertrophy. Male Sprague-Dawley rats underwent stenosis of the
abdominal aorta (hypertensive, HT) or sham operation (normotensive,
NT). Echocardiography and isolated left ventricular cardiomyocyte
dimensions demonstrated cardiac hypertrophy in the HT rats after 30 wk.
Cardiomyocyte microtubule fraction was assayed by high-speed
centrifugation and Western blot. In contrast to previous reports of
increased microtubules after acute pressure overload, microtubule
fraction for HT was significantly lower than that for NT.
Cardiomyocytes were exposed to either 1 µM colchicine, 10 µM taxol,
or equivalent volume of vehicle. Colchicine decreased microtubules, and
taxol increased microtubules in both groups. Cardiomyocyte cytosolic calcium
([Ca2+]c)
and shortening/relaxation dynamics were assessed during exposure to
increasing isoproterenol concentrations. The
-adrenergic response for these variables in the HT group was blunted compared with NT.
However, increased microtubule assembly by taxol partially recovered
the normal
-adrenergic response for time to peak
[Ca2+]c,
time to peak shortening, and mechanical relaxation variables. Microtubule assembly may play a significant role in determining cardiomyocyte
-adrenergic response in chronic cardiac hypertrophy.
signal transduction; cytoskeleton; taxol; colchicine; fura 2
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