Fibroblasts, myofibroblasts, and fibrosis: fact, fiction, and the future.

Fibroblasts and their activated phenotype known as myofibroblasts are nonexcitable cells found in all organs of the body. In the heart, fibroblasts, along with the endothelial and smooth muscle cells of the blood vessels, make up approximately 30% of tissue mass. In vitro, myofibroblasts cocultured with cardiac myocytes can propagate electrical signals down cellular strands indicating that under these conditions myofibroblasts are capable of depolarizing enough to maintain electrical propagation. This has obvious implications for cardiac biology if heterocellular coupling between fibroblasts and myocytes were to occur in the intact heart either under normal conditions or during cellular stress. The purpose of this review series is to highlight the newest information on cardiac fibroblasts and myofibroblasts and to review the data on their interactions with cardiac myocytes.