MORPHOMETRY OF MYOFIBRILES AND CONCLUSIVE APPARATUS IN THE PERIOD OF POSTPATAL MATURATION OF CARDIOMYOCYTES

Abstract

After 15 days of postnatal development of rats, in cardiomyocytes (CMC) of the left ventricle there is a longitudinal splitting of myofibrils, which leads to an increase in their number in the contractile apparatus (CA). In newborn (n/b) rats, the number of myofibrils (MF) in the contractile apparatus of the cardiomyocytic (CMC) does not exceed 12-13 pieces. In the CMC of 45-day-old animals, this figure is 80 pieces. If we take the thrust of one CMC of newborn rats, for one conventional unit Fcmc (n/b) = 1conditional unit (c.u.). The thrust of one CMC of 45-dayold rats will be equal to Fcmc = (80 MF: 12 MF) ≈ 6.5 c.u. conditional unit. Thus, the total thrust of all CMC (Ncmc = 0.72 x 107 ) in the myocardium of newborn rats theoretically is ∑Fcmc = 0.72 x 107 c.u. The traction force of all CMC (Ncmc = 1.56 x 107 ) in the myocardium of 45 day-old rats will be: ∑Fcmc = 1.56 x 107 х 6.5 c.u ≈ 108 c.u In the time interval (n/b) – 45 days, there is a fluctuation of digital values of the cross-sectional area of the MF in the narrow range SØmf ϵ[0.65-1.05] μm2 . “Increase ↔ decrease” of the volume of sarcomeres in the MF occurs as result of fluctuations in the composition of each sarcomere of the number of structural elements – hundreds. In the center of the honeycomb is one thick, and around the perimeter of 12 thin filaments. Six thin filaments area ttached to the Z-disk on one side of the thick filament, the other six to the Z-disk on the other side of the thick filament. The area of one cell is 6,225 х 10-4 μm2 . During the period of postnatal maturation of the CMC (45 days), the number of cells in the sarcomere ranges from 1044 to 1690. Thus, in the time interval (n/r – 45) days of postnatal maturation of the CMC, the increase in the absolute volume of the contractile apparatus of the CMC occurs under the influence of the following intracellular mechanisms. 1. Increasing the length of myofibrils in 3.2 times from 25 μm to 81 μm. 2. Increasing the number of MF in the contractile apparatus of cardiomyocytes in ≈ 6.5 times from 12-13 pieces to 80 pieces. 3. Fluctuations in the cross-sectional area of myofibrils in the range [0,65-1,05] μm2 . 4. Neoplasms of honeycombs – structural and functional units in the sarcomere from 1044 to 1690 pieces. As a result of increasing the number of CMC in ≈ 2.17 times and the number of myofibrils in each CMC in ≈ 6.7 times there is an increase in the contractile force of myocardial traction in 14 times.

Keywords

• cardiogenesis
• morphometry
• contractile apparatus
• cardiomyocyte.