Contractile proteins in pericytes. I. Immunoperoxidase localization of tropomyosin.

Abstract

The relative amounts and isoforms of tropomyosin were compared in capillary and postcapillary venule pericytes, endothelial cells and vascular smooth muscle cells in 4 rat microvascular beds: heart, diaphragm, pancreas and the intestinal mucosa. The results, obtained by in situ immunoperoxidase localization, indicate that tropomysin is present in capillary and postcapillary venule pericytes in relatively high concentration; the tropomyosin content of pericytes appears to be somewhat lower than in vascular smooth muscle cells but higher than in endothelia andother vessel-associated cells; and pericytes, unlike endothelia and other nonmuscle cells, contain detectable levels of tropomyosin immunologically related to the smooth muscle isoform. These results and previous findings concerning the presence of a cGMP-dependent protein kinase in pericytes demonstrate that these cells contain significant amounts of at least 2 proteins important for contraction regulation. Taken together, the evidence suggests that pericytes are contractile elements related to vascular smooth muscle cells, possibly involved, as are the latter, in the regulation of blood flow through the microvasculature.