C YTOCHALASINS and phalloidins are two groups of small, naturally occurring organic molecules that bind to actin and alter its polymerization. They have been widely used to study the role of actin in biological processes and as models for actin-binding proteins. Functionally , cytochalasins resemble capping proteins, which block an end of actin filaments, nucleate polymerization, and shorten fi...

When the fungal metabolite cytochalasin B was added to McCoy cells, multinucleated giant cells developed. Monolayers of these cells proved as efficient as irradiated cells for the growth of three different serotypes of Chlamydia trachomatis and for the primary isolation of chlamydiae from clinical specimens obtained from patients attending a venereal disease clinic. Cytochalasin treatment of Mc...

Low concentrations (0.5-1 microM) of cytochalasins inhibit the thrombin-stimulated polymerization of monomeric actin to filamentous actin in platelets. Similar concentrations of cytochalasin B inhibit the formation and metabolism of arachidonic acid in horse platelets stimulated by low concentrations of thrombin (0.1-0.5 unit/ml). However, the release of serotonin is not inhibited by cytochalas...

Human peripheral blood leukocytes (PMN) are induced to release lysosomal enzymes by the calcium ionophore A23187 in the presence but not the absence of extracellular Ca++. Whereas secretion induced by particulate or immune stimuli is accompanied by an increase in visible microtubules and is inhibitable by colchicine, secretion induced by A23187 and Ca++ was not accompanied by an increase in mic...

The widespread assumption that cytoplasts generated from human polymorphonuclear leukocytes (PMNs) are vesicles consisting solely of cytoplasm surrounded by plasma membrane and devoid of granule activity remains to be tested. PMN cytoplasts were prepared by centrifugation of intact cells on a Ficoll step gradient in the presence of cytochalasin B. Two granule membrane markers, Mol, a fluorometr...

We have previously described the isolation of a mutant KB cell (Cyt 1 mutant) resistant to the cytotoxic effect of cytochalasin B (CB). The Cyt 1 mutant carries an altered form of beta-actin (beta'-actin) and lacks normal beta-actin (Toyama, S., and S. Toyama. 1984. Cell. 37:609-614). Increased resistance of the Cyt 1 mutant to CB in vivo is reflected in altered properties of beta'-actin in vit...

Wortmannin, a selective inhibitor of phosphatidylinositol 3-kinase (P13K), was found to give a dose and time-dependent, bimodal effect-initial increase, followed by decrease on the tight junction integrity of MDCK-1 monolayers, as assessed by electrical resistance measurement of the epithelia. Moreover, dihydrocytochalasin B inhibited the wortmannin-induced alteration, whereas cytochalasin B ha...