Abstract
Objective:This study was performed to determine the effect of myosin light chain kinase (MLCK) inhibition on histamine- and thrombin-induced venular permeability in the rat mesentery, coincidental with actin cytoskeleton changes. Methods:The mesenteric microvasculature of rats was perfused with a fluorescent tracer plus thrombin, histamine, or buffered saline, and the preparation was suffused with the MLCK inhibitor ML-7. The microvasculature then was stained for actin. Results:The average (±SE) number of leaks per micrometer of venule length of the thrombin plus 5 µM ML-7 treatment (35.3 ± 5.9 × 10−4; n= 224) was significantly lower than that for the thrombin-only treatment (61.7 ± 5.6 × 10−4; n= 385; p< 0.001). The histamine preparations required higher concentrations of ML-7 to significantly reduce the number of leaks. A concentration of 100 µM reduced the average leak number from 20.8 ± 3.9 × 10 4(n= 140) to 2.5 ± 0.8 × 10−4(n= 383; p< 0.001), but 20 µM ML-7 had no effect. Although leaky areas of both the thrombin- and histamine-treated preparations showed disruptions of the peripheral actin rim coincident with fluorescein isothiocyanate-bovine serum albumin leaks, qualitative and quantitative differences were identified. Conclusions:The results suggest both similar and dissimilar mechanisms for thrombin and histamine regarding in situendothelial gap formation. Microcirculation(2003) 10,411–420. doi:10.1038/sj.mn.7800202