HETEROGENEITY OF SMOOTH MUSCLE-ASSOCIATED PROTEINS IN MAMMALIAN BRAINMICROVASCULATURE

In the brain, the microvascular system is composed of endothelial cell s surrounded by a layer of pericytes. The lack of smooth muscle cells in this tissue suggests that any contractile function must be performe d by one or both of these cell types. The present study was undertaken in order to identify cells in terminal blood vessels that contain smo oth muscle-like contractile machinery. Endothelial cells were reactive with antibodies against smooth muscle myosin but showed no other smoo th muscle-related features. In contrast, pericytes of intact microvess els showed a pattern of protein expression similar to that of smooth m uscle cells. Pericytes also behaved in tissue culture like cultured sm ooth muscle cells, with regard to the changes in expression of smooth muscle-related proteins. These data confirm the close relationship bet ween smooth muscle cells and pericytes, and point to their contractile function in the brain microvessels.