Regeneration of rat cardiac myocytes in vitro: colonies of сontracting neonatal cardiomyocytes

In parallel to the hypertrophy of major cardiac myocyte
population, we detected immunohistochemically the formation
of colonies consisting of small (dm = 6,20,5 ƒm) resident
c-kit+ and Sca+ stem cells (SC) and Isl1+-positive cardiac
myocyte progenitors (CMP) in the primary culture of neonatal
rat cardiac myocytes. First contracting colonies (~1-2
clones per 100000 cells) were registered starting from 8th
day of culture. The cells of the colonies were capable of spontaneous
differentiation, demonstrating the maturation of contractile
machinery and Ca2+ responses caffeine (5 мМ) and
K+ (120 мМ). The full-scale development of electromechanical
coupling with typical for cardiac muscle Ca2+-induced Ca2+
release was obvious at 3 weeks of culture. At first, the local,
weak, spontaneous, asynchronous, and arrhythmic contractions
at a rate of 2-3 beats/min were registered. However,
with time the contractions became synchronous and involved
all cells of the colony with the rate of contractions being
58-60 beats/min at the end of the month. First contracting
clones comprised Isl1+ CMP, while c-kit+-colonies started to
contract 9-10 days later possibly owing to a more prolonged
period of proliferation.
Thus, we first demonstrated and characterized the
contracting colonies originating from SC and CMP when
those were co-cultivated with mature cardiac myocytes.
The process described in this study is akin to regenerative
cardiomyogenesis encompassing the pathway from resident
progenitor cell to the colony of mature contracting cardiac
myocytes. It follows, therefore, that contracting myocyte
colony is a suitable model for basic research, testing of drugs,
and the investigation of regenerative capacity of SC and CMP
aimed at future applications of resident progenitor cells in
cell-based treatment of cardiac injury.