Figure 6. Structure of cardiomyocyte colonies grown in the primary culture of rat neonatal myocardial cells. (A–C) Different stages of development of the colonies stemming from Isl1⁺ CSCs. (A) Cell division, DIV 2. Isl1⁺ (FITC, green), GATA-4 (phycoerythrin, red). (B) Colony consisting of approximately 8 cells, DIV 11. Isl1⁺ (FITC, green), actin (rhodamine-phalloidin, red). (C) Large Isl1⁺ colony, DIV 11. Isl1⁺ (FITC, green), actin (rhodamine-phalloidin, red). (D) The optical sections of colonies formed by Isl1⁺, c-kit⁺, and Sca1⁺ CSCs on the 11th DIV. Isl1⁺ CSCs (Alexa 405, blue), Z = 12. c-kit⁺ CSCs (FITC, green), Z = 12. Sca1⁺ CSCs (Alexa 405, blue), Z = 11. Actin was stained using rhodamine-phalloidin (red). (E) Differentiation of c-kit⁺ CSCs inside the colony on the 13th DIV. Overlaid optical section of transmitted light and fluorescent images in 2 emitting wavelengths: 488 nm (FITC) and 543 nm (Alexa) in the bottom (Z = 5), in the middle (Z = 10), and the top (Z = 20) parts of the colony. c-kit⁺ expression was revealed by FITC-conjugated antibodies (green), and α-sarcomeric actinin was revealed by Alexa-conjugated antibodies (red). Confocal microscope, Leica TCS SP5 (Germany), objective ×63, oil.