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

Abstract

In parallel to the hypertrophy of major cardiac myocytepopulation, we detected immunohistochemically the formationof colonies consisting of small (dm = 6,20,5 ƒm) residentc-kit+ and Sca+ stem cells (SC) and Isl1+-positive cardiacmyocyte progenitors (CMP) in the primary culture of neonatalrat cardiac myocytes. First contracting colonies (~1-2clones per 100000 cells) were registered starting from 8thday of culture. The cells of the colonies were capable of spontaneousdifferentiation, demonstrating the maturation of contractilemachinery and Ca2+ responses caffeine (5 мМ) andK+ (120 мМ). The full-scale development of electromechanicalcoupling 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 contractionsat a rate of 2-3 beats/min were registered. However,with time the contractions became synchronous and involvedall cells of the colony with the rate of contractions being58-60 beats/min at the end of the month. First contractingclones comprised Isl1+ CMP, while c-kit+-colonies started tocontract 9-10 days later possibly owing to a more prolongedperiod of proliferation.Thus, we first demonstrated and characterized thecontracting colonies originating from SC and CMP whenthose were co-cultivated with mature cardiac myocytes.The process described in this study is akin to regenerativecardiomyogenesis encompassing the pathway from residentprogenitor cell to the colony of mature contracting cardiacmyocytes. It follows, therefore, that contracting myocytecolony is a suitable model for basic research, testing of drugs,and the investigation of regenerative capacity of SC and CMPaimed at future applications of resident progenitor cells incell-based treatment of cardiac injury.

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