CHANGES IN ENDOTHELIAL ACTIN CYTOSKELETON IN VENULES WITH TIME AFTER HISTAMINE TREATMENT

In this study the time course of development-and recovery of histamine-induced venular leaks was followed in conjunction with rearrangement of endothelial actin fibers. The microvasculature of a single mesenteric window of anesthetized Sprague-Dawley rats was perfused with buffered saline, with or without 10(-4) M histamine, for 3-30 min. Fluoroscein isothiocyanate (FITC)-albumin was added for the last 3 min. The microvasculature was perfusion fixed, stained with rhodamine phalloidin (for filamentous actin), and viewed using confocal microscopy. The number and relative size of FITC-albumin leaks per venule length were measured. After 3 min of histamine application focal leaks appeared in some of the venules. Most focal leaks were accompanied by local breaks in the endothelial peripheral actin rim. Larger leaks were also present, accompanied by greater disruption of the venular endothelial peripheral actin rim, diffuse F-actin staining, and adherent platelets and leukocytes. Few central actin fibers were visible even in endothelial cells associated with large leaks. After 10-15 min of histamine exposure, larger leaks were more abundant but with fewer adherent cells. Central actin fibers in endothelial cells increased in number, peaking after 20 min of histamine, while the diffuse actin staining declined. Leak area per micrometer of venule peaked at 10-15 min, but the numbers of leaks per micrometer did not vary significantly from 3 to 30 min. These data suggest that the central fibers are not involved with the phase of increasing permeability, but they may play a role in the structural and functional recovery of endothelial cells perturbed by histamine.