MULTIPLE PHENOTYPICALLY DISTINCT SMOOTH-MUSCLE CELL-POPULATIONS EXISTIN THE ADULT AND DEVELOPING BOVINE PULMONARY ARTERIAL MEDIA IN-VIVO

Different smooth muscle cell (SMC) functions may require different cel l phenotypes. Because the main pulmonary artery performs diverse funct ions, we hypothesized that it would contain heterogeneous SMC populati ons. If the hypothesis were confirmed, we wished to determine the deve lopmental origin of the different populations. Using specific antibodi es, we analyzed the expression of smooth muscle (SM) contractile and c ytoskeletal proteins (Lu-SM-actin, SM myosin, calponin, desmin, and me ta-vinculin) in the main pulmonary artery of fetal (60 to 270 days of gestation), neonatal, and adult animals. We demonstrated the existence of a complex, site-specific heterogeneity in the structure and cellul ar composition of the pulmonary arterial wall. We found that at least four cell/SMC phenotypes, based on immunobiochemical characteristics, cell morphology, and elastic lamellae arrangement pattern, were simult aneously expressed within the mature arterial media. Further, we were able to assess phenotypic alterations in each of the four identified c ell populations during development. We found that each cell population certain stages of development, thus demonstrating its smooth muscle i dentity. However, each cell population progressed along different deve lopmental pathways, suggesting the existence of multiple and distinct cell lineages. A novel anti-metavinculin antibody described in this st udy reliably distinguished one SMC population from the others during a ll the developmental stages analyzed. We conclude that the pulmonary a rterial media is indeed composed of multiple phenotypically distinct c ell/SMC populations with unique lineages. We speculate that these dist inct cell populations may serve different functions within the arteria l media and may also respond in unique ways to pathophysiological stim uli.