AJP - Heart and Circulatory Physiology, Vol 251, Issue 6 1118-H1125, Copyright © 1986 by American Physiological Society
Microtubule reorganization is related to rate of heart myocyte hypertrophy in rat
J. L. Samuel, F. Marotte, C. Delcayre and L. Rappaport
Since stimulation of heart hypertrophy by pressure overload was previously
shown to be accompanied by a densification of microtubule network in rat
heart myocytes, we verified that similar process occurred during postnatal
growth in euthyroid rats and in hypothyroid rats whose growth was
stimulated by 4 micrograms/day L-thyroxine (T4). For this purpose, tubulin,
the constituent protein of microtubules, was immunolabeled in myocytes
isolated at various times after birth. Myocyte hypertrophy was evaluated by
myocyte size, the number of nuclei per cell and isomyosin expression. In
hypothyroid rats, the microtubule network, which was underdeveloped, was
most dense around the nucleus. During the phase of fast myocyte hypertrophy
observed in euthyroid rats during late postnatal development and in
hypothyroid rats after T4 administration, transient microtubule
densification occurred in a myocyte subpopulation in which size was mainly
determined by the rate of myocyte hypertrophy. The densification process
and its kinetics resembled those observed when heart hypertrophy was
induced by pressure overload. It is concluded that in rat heart myocytes
undergoing hypertrophy, microtubule densification might be related to fast
sarcomerogenesis, whether the stimulus is mechanical (e.g., pressure
overload) or hormonal (e.g., T4).
