Expression of myocyte-specific markers by hMSCs co-cultured with Cor.AT cells. (A) 14 days co-culture (1-3) Co-culture in CorAT medium supplemented with components of differentiation cocktail, (4-6) co-culture in Cor.AT medium: 1 and 4 - immunofluorescent staining; 2 and 5 - same field, green coloured cells - murine atrial-like cardiomyocytes (Cor.AT cells) expressing GFP; 3 and 6 - merged. (a) GATA4, (b) connexin-43, (c) Nkx2.5, (d) myoglobin (differentiated hMSCs showing organized myoglobin structure are marked with a blue star), (e) cardiac troponin I, (f) cardiac myosin heavy chain, (g) CD44. Scale bar is 100 μm. (B) Detection of connexin-43 in 25 days co-culture (1-3) Co-culture in CorAT medium supplemented with components of differentiation cocktail, (4-6) co-culture in Cor.AT medium: 1 and 4 - immunofluorescent staining; 2 and 5 - same field, green coloured cells - murine atrial-like cardiomyocytes (Cor.AT cells) expressing GFP; 3 and 6 - merged. (a) and (b) detection of connexin-43 in two independent assays after 25 days. Scale bar is 100 μm.