Formation of Actin Clusters in Rat Liver Parenchymal Cells on Phalloidin Poisoning as Visualized by a Fluorescent Phallotoxin

Abstract

By staining of cryo-sections of rat liver with a fluorescent phallotoxin, the distribution of filamentous actin in liver cells could be demonstrated by fluorescence microscopy. While in untreated livers filamentous actin forms an almost continous layer at the cell periphery, the poisoning by phalloidin leads to the formation of actin clusters, preferentially located near the cell membrane.

Changes in the localization of the rat canalicular conjugate export pump mrp2 in phalloidin-induced cholestasis

“…9 We therefore hypothesized that changes in actin filament organization would rather alter the localization and distribution of canalicular transport proteins as shown in other forms of intrahepatic cholestasis. 16 In agreement with previous findings, 35 we show that a single administration of phalloidin leads to markedly altered actin organization ( Fig. 2B) and to cholestasis (Fig.…”

“…These morphological changes may correspond to the invaginations of the canalicular membrane and to the pericanalicular vacuoles described by other investigators early after phalloidin poisoning. 35,39,40 At the onset of these changes, the Mrp2-containing membrane structures were close to the canaliculi. Later after phalloidin administration, Mrp2-containing remnants were also found within the hepatocytes and had no visible contact to the canalicular membrane.…”

“…After intravenous administration, phalloidin is preferentially transported into the hepatocytes 41 where it binds to actin and stabilizes actin filaments. 42,43 Phalloidin-induced changes involve actin aggregation, 35,44 alteration of the pericanalicular actomyosin complex, 40,45 and displacement of the subplasmalemmal microfilaments. 35 This leaves domains of the cell membrane partly separated from the normal microfilament web 2,40 and leads to gaps in the cortical actin ring.…”

“…42,43 Phalloidin-induced changes involve actin aggregation, 35,44 alteration of the pericanalicular actomyosin complex, 40,45 and displacement of the subplasmalemmal microfilaments. 35 This leaves domains of the cell membrane partly separated from the normal microfilament web 2,40 and leads to gaps in the cortical actin ring. Alteration of pericanalicular actin organization inhibits canalicular contraction 32 but by itself does not necessarily affect the function of canalicular export pumps.…”

Fluorescent phallotoxins as probes for filamentous actin

“…Haemorrhagia is accompanied by an abnormal clustering of actin, presumably mediated by phalloidin in the cortical filamentous network of hepatocytes (Jahn et al, 1980). Additionally, phalloidin disturbs the Ca 2+ homeostasis of hepatocytes which, in turn, may influence the activity of Ca2+-regulated actin-binding proteins through a transient rise of intracellular Ca 2+ (Faulstich & M~inter, 1986).…”