THE ALPHA-SMOOTH MUSCLE ACTIN-POSITIVE CELLS IN HEALING HUMAN MYOCARDIAL SCARS

Interstitial cells in the scars of human myocardial infarctions of dif ferent postinfarction times (6 hours to 17 years old) were characteriz ed by antibodies to alpha-smooth muscle actin (ASMA), vimentin, and de smin. Basal lamina deposition was studied with antibodies to the basal lamina protein type IV collagen. Nonvascular spindle-shaped cells exp ressing ASMA were present within 4 to 6 days after infarction These ce lls co-expressed vimentin but no desmin and showed discontinuous basal lamina deposition. In electron microscopy these cells showed features characteristic of myofibroblasts. The spindle-shaped cells persisted for a long period of time and could even be identified 17 years postin farction. In transmural infarctions they were orientated parallel to t he endocardium and epicardium. In nontransmural patchy infarctions the y showed an orientation adjacent to the cardiomyocytes and appeared to be less dense than in the transmural infarctions. In conclusion, myof ibroblasts expressing ASMA persist within human myocardial scars and s how a preferential alignment that may be the result of the continuous mechanical stress caused by the ongoing contraction and relaxation of the surrounding viable myocardium.