Abstract
Objective:Active constriction in cardiac capillary endothelial cells (CCECs) is controversial. It is thought by many researchers that CCECs are not actively involved in constriction; others believe that these cells do contribute some of the force required for capillary constriction. Because actin is a major component of most contractile mechanisms responsible for changing cell shape, we compared two probes as potential monitors of actin distribution in CCECs in situ. Methods:We used SDS-PAGE, Western blotting, electron microscopy, conventional epifluorescence and confocal microscopy to evaluate an antibody against non-muscle β-actin and fluorescently labeled phalloidin to detect actin in CCECs. Results:Fluorescently labeled phalloidin detected actin in cardiac muscle and faintly in CCECs. The antibody probe detected non-muscle β-actin in CCECs. However, this actin isotype did not occur in cardiac myocytes. In endothelial cells non-muscle β-actin was concentrated at the cell periphery, and arranged as bundles of fibers, not as typical stress fibers. Conclusions:Phalloidin is not suitable as a probe to monitor actin distribution in CCEC's in situ. The antibody is a potentially useful tool in monitoring the actin cytoskeleton and determining the capacity of CCECs for active vasoconstriction in vivo. Non-muscle β-actin in CCECs is arranged in filament bundles which are not typical stress fibers.