Regeneration of rat cardiac myocytes in vitro: the proliferative activity of neonatal cardiac myocytes

In mammalian heart, cardiac myocyte division ceases within
the first week of postnatal life posing one of the most intriguing
questions of evolution. Stimulation of cardiac myocyte proliferation
during postnatal period would have profound impact on cardiac
regeneration in humans. It has been shown that the primary
culture of cardiac myocytes obtained from newborn rat could
serve as an appropriate model for the investigation of the processes
taking place in the heart during early postnatal ontogenesis.
Similarly to the in vivo situation, the increased mitotic activity
observed during the first 2-4 days after birth is diminished in
cardiac myocyte culture within 4-5 days of culturing. Besides,
60% of cultured cells underwent mitotic division followed by increase
in their volume which also closely resembles the process
of cardiac myocyte hypertrophy in vivo. The cardiac myocyte volume
was progressively increased during culturing and equaled to
81968, 1532212, and 3246190 ƒm3 on the 1st, 3rd, and
6th day of culture, respectively. Furthermore, the rate of cardiac
myocyte growth in culture was similar to the pattern of myocyte
hypertrophy observed in the in vivo settings. Myocyte hypertrophy
in culture was associated with the formation of polyploid and
multinucleated, most commonly binucleated, cells which is generally
analogous to the in vivo myocyte hypertrophy. The analysis
of myocyte volume distribution suggested that during cultivation
nearly 60% of cells are switched from hyperplasia to hypertrophy,
stopping at the G2/M boundary of the cell cycle.
The results obtained indicate that cell growth patterns in
primary cardiac myocyte culture share a lot of similarity with the
in vivo cardiac myocyte growth. Primary cardiac myocyte culture
is a valuable tool for investigation of the processes responsible
for cessation of cardiac myocyte division in adult mammals.