Relative Potencies of Different Cytochalasins for the Inhibition of Phagocytosis in Ciliates

Abstract

Ciliate actins have been reported to exhibit an unusual degree of sequence divergence, within the phylum Ciliophora, and when compared to actins from other organisms. To determine whether these primary structural differences are correlated with pharmacological differences, we investigated the effects of seven cytochalasins on phagocytosis, which has been shown to be actin‐dependent in eukaryotic cells. The relative potencies of cytochalasin inhibition of phagocytosis in Spirostomun ambiguum and Paramecium multimicronucleatum were similar. Dihydrocytochalasin B and cytochalasin A were the most potent of the seven cytochalasins in both ciliates, and strongly inhibited phagocytosis at 20‐40 μM. Dihydrocytochalasin B was considerably more potent than either cytochalasins B or D, a result unexpected on the basis of reports utilizing other organisms. However, even at concentrations up to 100 μM, dihydrocytochalasin B did not inhibit the rate of Spirostomum defecation. After long‐term treatment of Spirostomum with 50 μM dihydrocytochalasin B, the sensitivity of phagocytosis to the drug was reduced. These results indicate that the relative cytochalasin sensitivities of actin‐dependent functions in ciliates differ from those of other organisms, and are consistent with the hypothesis that sequence differences might give rise to substantial differences in the pharmacological properties of ciliate actins.

Induction of Anti‐Actin Drug Resistance in Tetrahymena

“…Thus, LAT‐B is approximately 10 times more potent than CD for inhibition of Tetrahymena phagocytosis. As was previously described in a variety of ciliates treated with cytochalasins (Allen and Fok 1985; Fok et al 1985; Cohen, Garreau de Loubressa, and Beisson 1984; Nilsson 1977; Zackroff and Hufnagel 1998), micromolar concentrations of both CD and LAT‐B blocked phagosome release from the cytostome and frequently resulted in formation of an oversized, open phagosome which persisted for the duration of the assay. The effects of LAT‐B on Tetrahymena phagocytosis were fully reversible within 15 min of drug removal by low speed centrifugation (not shown).…”

Development of a Fluorescent Multiwell Assay for Evaluating the Capacity of the Ciliated Protozoan Tetrahymena for Bacterivory in Water Samples

“…2). Third, Cytochalasin B, which is known to block the formation of phagosomes in Tetrahymena (Nilsson 1977;Zackroff and Hufnagel 1998), prevented the decrease in RFUs (Fig. 4).…”

“…As phagocytosis in ciliates and other eukaryotic cells is dependent on actin and inhibited by actin-disrupting drugs such as cytochalasins (Nilsson 1977;Zackroff and Hufnagel 1998), the capacity of T. thermophila to reduce the fluorescence in co-cultures with E. coli XL-1 (pET-gfp) was examined at different Cytochalasin B concentrations. Cytochalasin B was found to inhibit the decrease in RFU in a dose-dependent manner (Fig.…”

Calcium in ciliated protozoa: Sources, regulation, and calcium-regulated cell functions

“…Localization of actin and myosin to ciliary basal bodies may entail a novel regulatory aspect (as unexpected as the discovery of kinesin in cilia). Because the sensitivity of ciliates to otherwise established drugs, like cytochalasins, may deviate greatly from that of mammalian cells (Zackroff and Hufnagel, 1998), it appears advisable in future work to take advantage of gene cloning and the production of more specific ABs.…”