Expression of nonmuscle myosin heavy chain-B isoform in the vessel wall of porcine coronary arteries after balloon angioplasty.

Nonmuscle myosin heavy chain-B isoform (NMMHC-B) is expressed by proliferating vascular smooth muscle cells (SMCs), and its expression in primary lesions has been proposed to be predictive of restenosis after atherectomy. The present study was designed to study the time-course expression of NMMHC-B after angioplasty of porcine coronary arteries by in situ hybridization and immunohistochemistry. Domestic juvenile swine underwent percutaneous transluminal coronary angioplasty (PTCA) of the left anterior descending and circumflex coronary arteries with standard clinical angioplasty catheters. To identify proliferating cells, 5'-bromo-2'-deoxyuridine (BrdU) was administered and detected by immunohistochemistry on serial sections. Vessels were examined at 3, 7, and 14 days after balloon angioplasty, and uninjured coronary vessels were used as controls. Normal arteries showed hybridization to 35S-labeled NMMHC-B riboprobes localized mainly in the medial layer. NMMHC-B expression in the adventitia was markedly increased 3 days after balloon angioplasty. Seven and 14 days after injury, NMMHC-B mRNA-containing cells were localized in the adventitia and neointima at the arterial injury site. Cell proliferation, as indicated by BrdU staining, colocalized with NMMHC-B mRNA expression 3 and 7 days after angioplasty. These data indicate that cells proliferating in the adventitia and neointima express NMMHC-B; however, its expression is not limited to the proliferative state, since NMMHC-B mRNA was also found in quiescent SMCs of normal coronary arteries and in nonproliferating adventitial and neointimal cells 14 days after angioplasty.