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 mesenter ic window of anesthetized Sprague-Dawley rats was perfused with buffer ed saline, with or without 10(-4) M histamine, for 3-30 min. Fluorosce in isothiocyanate (FITC)-albumin was added for the last 3 min. The mic rovasculature was perfusion fixed, stained with rhodamine phalloidin ( for filamentous actin), and viewed using confocal microscopy. The numb er and relative size of FITC-albumin leaks per venule length were meas ured. After 3 min of histamine application focal leaks appeared in som e 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 peripher al actin rim, diffuse F-actin staining, and adherent platelets and leu kocytes. Few central actin fibers were visible even in endothelial cel ls associated with large leaks. After 10-15 min of histamine exposure, larger leaks were more abundant but with fewer adherent cells. Centra l 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. Thes e data suggest that the central fibers are not involved with the phase of increasing permeability, but they may play a role in the structura l and functional recovery of endothelial cells perturbed by histamine.