Role of the actin cytoskeleton in regulating endothelial permeability in venules.
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 microM ML-7 treatment (35.3 +/- 5.9 x 10(-4); n = 224) was significantly lower than that for the thrombin-only treatment (61.7 +/- 5.6 x 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 microM reduced the average leak number from 20.8 +/- 3.9 x 10(-4) (n = 140) to 2.5 +/- 0.8 x 10(-4) (n = 383; p < 0.001), but 20 microM 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 situ endothelial gap formation.
Valeski
J Edward
JE
Department of Physiology, College of Medicine, University of Arizona, Tucson, AZ 85724-5051, USA. valeski@u.arizona.edu
Baldwin
Ann L
AL
D000199:Actins / Q000502:physiology*; D000818:Animals; D001381:Azepines / Q000494:pharmacology; D002199:Capillary Permeability / Q000187:drug effects / Q000502:physiology*; D003599:Cytoskeleton / Q000187:drug effects / Q000502:physiology*; D004730:Endothelium, Vascular / Q000187:drug effects / Q000502:physiology*; D004791:Enzyme Inhibitors / Q000494:pharmacology; D006632:Histamine / Q000494:pharmacology; D008297:Male; D008642:Mesenteric Veins / Q000187:drug effects / Q000502:physiology; D008856:Microscopy, Fluorescence; D009219:Myosin-Light-Chain Kinase / Q000037:antagonists & inhibitors; D009281:Naphthalenes / Q000494:pharmacology; D051381:Rats; D017207:Rats, Sprague-Dawley; D013917:Thrombin / Q000494:pharmacology; D014699:Venules / Q000187:drug effects / Q000502:physiology
D000199:Actins; D001381:Azepines; D004791:Enzyme Inhibitors; D009281:Naphthalenes; C070571:ML 7; D006632:Histamine; D009219:Myosin-Light-Chain Kinase; D013917:Thrombin