CLINICAL STUDIES
Role of microtubules in the contractile dysfunction of hypertrophied myocardium
Michael R. Zile, MD, FACC*,
Masaaki Koide, MD*,
Hiroshi Sato, MD*,
Yoshiki Ishiguro, MD ,
Chester H. Conrad, MD, PhD ,
J. Michael Buckley, MS*,
James P. Morgan, MD, PhD, FACC and
George Cooper, IV, MD*
* Cardiology Section of the Department of Medicine and the Department of Physiology, Gazes Cardiac Research Institute, Medical University of South Carolina, and the Veterans Administration Medical Center, Charleston, South Carolina, USA
Veterans Administration Medical Center, Boston, Massachusetts, USA
Beth Israel Deaconess Medical Center, Boston, Massachusetts, USA
Manuscript received June 23, 1998;
revised manuscript received August 6, 1998,
accepted September 4, 1998.
Address for correspondence: Dr. Michael R. Zile, Division of Cardiology, Medical University of South Carolina, 171 Ashley Avenue, Charleston, South Carolina 29425-5799
zilem{at}musc.edu
Objectives. We sought to determine whether the ameliorative effects of microtubule depolymerization on cellular contractile dysfunction in pressure overload cardiac hypertrophy apply at the tissue level.
Background. A selective and persistent increase in microtubule density causes decreased contractile function of cardiocytes from cats with hypertrophy produced by chronic right ventricular (RV) pressure overloading. Microtubule depolymerization by colchicine normalizes contractility in these isolated cardiocytes. However, whether these changes in cellular function might contribute to changes in function at the more highly integrated and complex cardiac tissue level was unknown.
Methods. Accordingly, RV papillary muscles were isolated from 25 cats with RV pressure overload hypertrophy induced by pulmonary artery banding (PAB) for 4 weeks and 25 control cats. Contractile state was measured using physiologically sequenced contractions before and 90 min after treatment with 10–5 mol/liter colchicine.
Results. The PAB significantly increased RV systolic pressure and the RV weight/body weight ratio in PAB; it significantly decreased developed tension from 59 ± 3 mN/mm2 in control to 25 ± 4 mN/mm2 in PAB, shortening extent from 0.21 ± 0.01 muscle lengths (ML) in control to 0.12 ± 0.01 ML in PAB, and shortening rate from 1.12 ± 0.07 ML/s in control to 0.55 ± 0.03 ML/s in PAB. Indirect immunofluorescence confocal microscopy showed that PAB muscles had a selective increase in microtubule density and that colchicine caused complete microtubule depolymerization in both control and PAB papillary muscles. Microtubule depolymerization normalized myocardial contractility in papillary muscles of PAB cats but did not alter contractility in control muscles.
Conclusions. Excess microtubule density, therefore, is equally important to both cellular and to myocardial contractile dysfunction caused by chronic, severe pressure-overload cardiac hypertrophy.
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Abbreviations and Acronyms
| | BDM | = 2,3-butanedione monoxime | | cAMP | = adenosine 3':5'-cyclic monophosphate | | IBMX | = 3-isobutyl-1-methylxanthine | | Lmax | = length for peak active tension | | LV | = left ventricular | | ML | = muscle length | | PAB | = pulmonary artery band | | POH | = pressure-overload hypertrophy | | RV | = right ventricular |
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