ULTRASTRUCTURAL ANALYSIS OF THE ROLE PLAYED BY MICROTUBULES IN THE TRANSPORT AND
EXOCYTOSIS OF PROTEINACEOUS SECRET IN THE MAMMARY SECRETORY CELLS
S. M. Popov,1 I. N. Pavlenko,1 G. B. Balakina,1
A. A. Kryukov,2 Ya. Yu. Komissarchik 2
1 The A. A. Ukhtomsky Physiological Institute, St. Petersburg State University, and
2 Institute of Cytology RAS, St. Petersburg, Russia;
e-mail: yykomis@mail.cytspb.rssi.ru
Morphometrical analysis of microtubules (MT) and coated vesicles (CV) was done on electron micrographs of the murine
mammary gland sections at the final stages of functional maturation of secretory cells (SC), as well as at different stages of the cell
secretory cycle (CSC). The results obtained allow to make the following conclusions: 1) dynamics of changes in the MT count in different
subplasmalemmal cell compartments is similar, being directly associated with heterochronical character of CSC processes;
2) the maximum MT count in SC was seen during formation of the secretion product, this increase occurring at the expense of short MT,
which are disassembled before and during exocytosis of secretory vesicle (SV) contents; 3) changes in the number of MT and CV are of
similar character, which was revealed by morphometrical analysis of SC in the course of maturation. The number of MT and CV in SC
increased rapidly and significantly on the 1 st and 2nd days after parturition, compared to that observed 1-2 days before parturition.
However, the number of MT and CV decreased by the 10th day of lactation, when the mammary secretory activity reached its maximum.
Both correlation and regression statistical analyses made during the CSC development point to a linear relation between MT (x) and CV (y)
numbers. Regression of ó on x is: ó = -0.89 + 12.43õ. A hypothesis about the possibility of MT participation in CV and SV transport and in
the formation of a barrier on the path leading to exocytosis of SV contents is suggested.
Key words: mammary secretory cells - maturation and secretory cycle, cytoskeleton system, microtubular functions,
coated and secretory vesicles
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