Localization of types I, III and IV collagen mRNAs in rat heart cells by in situ hybridization.

Previous studies investigating the cellular origins of several collagens in young adult rat hearts (Eghbali et al., 1988) demonstrated that the mRNAs for types I and III collagen occurred in non-myocyte cells, mostly fibroblasts, whereas the mRNA for type IV collagen was observed in both myocytes and non-myocyte cells. In the present study, cellular localization of collagen mRNAs has been achieved by in situ hybridization in rat heart tissue and in isolated heart cells. Frozen tissue sections, isolated cardiomyocytes, cultured neonatal cardiomyocytes and fibroblasts were hybridized with DNA probes for type-specific collagens, actin, and myosin heavy chain. Silver grains were visualized by dark field imaging. In heart sections, types I and III mRNAs were observed predominantly adjacent to myocytes and in the interstitium, where fibroblasts are known to be present. In contrast, type IV collagen mRNA was identified both within the myocytes and the interstitium. In freshly isolated adult cardiomyocytes and in cultured neonatal cardiomyocytes, collagen type IV mRNA was observed but type I collagen mRNA was not. In cultured neonatal fibroblasts, both types IV and I collagen mRNAs were abundant.