phalloidine and Carcinoma--Ehrlich-Tumor

The role of the F-actin cytoskeleton in cell volume regulation was studied in Ehrlich ascites tumor cells, using a quantitative rhodamine-phalloidin assay, confocal laser scanning microscopy, and electronic cell sizing. A hypotonic challenge (160 mOsm) was associated with a decrease in cellular F-actin content at 1 and 3 min and a hypertonic challenge (600 mOsm) with an increase in cellular F-actin content at 1, 3, and 5 min, respectively, compared to isotonic (310 mOsm) control cells. Confocal visualization of F-actin in fixed, intact Ehrlich cells demonstrated that osmotic challenges mainly affect the F-actin in the cortical region of the cells, with no visible changes in F-actin in other cell regions. The possible role of the F-actin cytoskeleton in RVD was studied using 0. 5 microM cytochalasin B (CB), cytochalasin D (CD), or chaetoglobosin C (ChtC), a cytochalasin analog with little or no affinity for F-actin. Recovery of cell volume after hypotonic swelling was slower in cells pretreated for 3 min with 0.5 microM CB, but not in CD- and ChtC-treated cells, compared to osmotically swollen control cells. Moreover, the maximal cell volume after swelling was decreased in CB-treated, but not in CD- or Chtc-treated cells. Following a hypertonic challenge imposed using the RVD/RVI protocol, recovery from cell shrinkage was slower in CB-treated, but not in CD- or Chtc-treated cells, whereas the minimal cell volume after shrinkage was unaltered by either of these treatments. It is concluded that osmotic cell swelling and shrinkage elicit a decrease and an increase in the F-actin content in Ehrlich cells, respectively. The RVD and RVI processes are inhibited by 0.5 microM CB, but not by 0.5 microM CD, which is more specific for actin.

Topics: Actins; Animals; Carcinoma, Ehrlich Tumor; Cell Size; Cytoskeleton; Fluorescent Dyes; Hypertonic Solutions; Hypotonic Solutions; Mice; Microscopy, Confocal; Osmotic Pressure; Phalloidine; Rhodamines; Tumor Cells, Cultured

Cyclosporin A inhibits the uptake of cholate into isolated hepatocytes in a non-competitive manner (Ki = 3.6 microM). It protects liver cells against phalloidin injury by a mixed competitive/non-competitive inhibition of phalloidin uptake (Ki = 0.08 microM). Rifampicin, a well-known substrate of the bilirubin transporter is also incorporated in a decreased quantity in the presence of cyclosporin A (IC50 = 80 microM). A photolabile diaziridine derivative of cyclosporin A was used for the identification of binding sites. In comparison with the original cyclosporin A the photoaffinity label exhibits a 2-3-fold lower affinity to the cholate (and phalloidin) transporter in the liver cell membrane. In the dark the label inhibits the uptake of both cholate and of phalloidin reversibly; after treatment with ultraviolet light flashes the inhibition becomes irreversible. The degree of inhibition is concentration dependent. Our results suggest binding of cyclosporin A to protein components of the cholate (and phalloidin) transporter of liver cells without uptake by this system. The inhibition of cholate (and phalloidin) uptake by cyclosporin A is non-competitive and may be due to nonspecific hydrophobic binding to compounds of the cholate transporter.

Topics: Aminoisobutyric Acids; Animals; Biological Transport; Carcinoma, Ehrlich Tumor; Cholic Acid; Cholic Acids; Cyclosporins; Kinetics; Liver; Mice; Oligopeptides; Phalloidine; Rifampin

Topics: Animals; Carcinoma, Ehrlich Tumor; Drug Tolerance; Male; Mice; Oligopeptides; Phalloidine

Topics: Agaricales; Amanita; Amanitins; Animals; Carcinoma, Ehrlich Tumor; Mice; Oligopeptides; Phalloidine; Plant Extracts; Rats; Sarcoma, Yoshida; Water