ISOLATION OF A MORPHOLOGICALLY AND FUNCTIONALLY DISTINCT SMOOTH-MUSCLE CELL-TYPE FROM THE INTIMAL ASPECT OF THE NORMAL RAT AORTA - EVIDENCEFOR SMOOTH-MUSCLE CELL HETEROGENEITY

Recent studies indicate that the neointima of injured rat arteries is composed of a subpopulation of smooth muscle cells (SMCs) distinct fro m medial smooth muscle cells. However, SMC diversity in normal adult a orta has remained elusive. This study characterizes two morphologicall y and functionally distinct SMC types isolated from different anatomic regions of the normal rat aorta. Rat aortic medial smooth muscle cell s (MSMCs) were isolated from the media after removal of the intimal an d adventitial cells. Rat aortic intimal smooth muscle cells (ISMCs) we re isolated from the intimal aspect of everted rat aortas. The two cel l types were characterized morphologically and immunohistochemically a nd were compared for their capacity to contract collagen gels in respo nse to endothelin-l. MSMCs were spindle-shaped and grew in hills and v alleys showing features previously described for vascular SMCs. Conver sely, ISMCs displayed a polygonal and epithelioid shape, grew mainly a s a monolayer, and had a higher proliferative rate. Both cell types ex pressed alpha-smooth muscle actin and were negative for Factor VIII-RA g. ISMCs produced large amounts of a laminin and type IV collagen-rich extracellular matrix which had a characteristic pericellular distribu tion. ISMCs, but not MSMCs, rapidly contracted collagen gels in respon se to endothelin-l. This study indicates that the normal rat aorta con tains two types of SMCs located in anatomically distinct regions of th e vessel wall. Because of their functional characteristics, the SMCs i solated from the intimal aspect of the aorta may play an important rol e in physiologic as well as pathologic conditions.