Immunoelectron microscopic evidence of contractile proteins in the cellular and acellular components of mouse kidney glomeruli

Actin and/or actin-like protein have been localized in the cellular and acellular components of the glomerular walls of mouse kidney by means of immunoelectron microscopy, employing human antibodies to smooth muscle (SMA). Contractile antigens have been confirmed to be present in the cytoplasm of podocytes and mesangial cells in association with fine filaments which are considered of importance in the control of blood flow, intravascular pressure, and filtration rate within the glomerulus. The extracellular presence of contractile proteins in the mesangial matrix and glomerular basement membrane can be related to cell movement in a frictional environment. This latter phenomenon, which is strictly interdependent with cell adhesion and aggregation, is most evident in the mesangial cells in a form of luminar pseudopodia, cytoplasmic projections, and phagocytosis.