MICROFILAMENT-DISRUPTING AGENT LATRUNCULIN-A INDUCES AN INCREASED NUMBER OF FENESTRAE IN RAT-LIVER SINUSOIDAL ENDOTHELIAL-CELLS - COMPARISON WITH CYTOCHALASIN-B

This report describes the effect of the actin-disrupting marine toxin latrunculin A on the cytoskeleton and fenestrae of Liver endothelial c ells (LECs), Fluorescence microscopy and whole mount-transmission elec tron microscopic preparations of isolated, purified, and cultured LECs showed that latrunculin A, which sequesters actin monomers and depoly merizes actin filaments, caused profound changes in microfilament orga nization in LECs. Scanning electron microscopic preparations showed th at latrunculin A almost doubles the number of fenestrae within 10 minu tes, whereas the diameter is only slightly reduced, All new fenestrae possess the earlier described fenestrae-associated cytoskeleton ring, Cytochalasin B, which disrupts the network of actin filaments, princip ally by capping the fast growing end of actin filaments, produced comp arable effects with regard to actin organization and the number and si ze of fenestrae, After 1 hour of treatment, an equal maximum number of fenestrae was observed for both agents. The effect of latrunculin A w as obtained at concentrations about 100 times lower than cytochalasin B, Thus, two agents that alter the state of actin organization in LECs , albeit by different mechanisms, cause the doubling of the number of fenestrae within 10 to 30 minutes, This indicates that the state of as sembly of the actin cytoskeleton is important in the numerical dynamic s of LEC fenestrae and that the actin cytoskeleton of LECs is probably the main mechanical regulator for sieving between the sinusoidal bloo d and the parenchymal cells, Latrunculin A represents a new agent in t he study of the de novo formation of fenestrae.