Concentration-dependent effects of cytochalasin D on tight junctions and actin filaments in MDCK epithelial cells.
The effects of different concentrations of the actin-disrupting drug cytochalasin D on tight junction permeability and distribution of actin filaments in MDCK epithelial cells were examined. Consistent with previous studies, 2 micrograms/ml cytochalasin D caused a significant decrease in transepithelial resistance, indicative of an increase in tight junction permeability. Surprisingly, increasing concentrations of cytochalasin D caused progressively smaller decreases in transepithelial resistance. The effects of cytochalasin D were reversible. Light microscopic analysis utilizing rhodamine-conjugated phalloidin demonstrated two distinct populations of actin filaments in MDCK cells: an apical peripheral ring of actin, presumably associated with the zonula adherens, and larger actin bundles more basally situated. When treated with 2 micrograms/ml cytochalasin D, both actin populations were severely disrupted and cells became flattened. Actin in the apical ring aggregated along cell boundaries, and these aggregates co-localized with similarly disrupted focal accumulations of the tight junction-associated protein ZO-1. The basal actin filament bundles also reorganized into focal aggregates. Increasing concentrations of cytochalasin D caused gradually less perturbation of the apical actin ring, consistent with the transepithelial resistance observations. However, the basal actin bundles were disrupted at all concentrations of cytochalasin D tested, demonstrating that the two actin populations are differentially sensitive to cytochalasin D and that apical actin filaments are more important in the regulation of tight junction permeability. Finally, treatment of cells with cytochalasin D inhibited the decrease in transepithelial resistance induced by the chelation of extracellular Ca2+.(ABSTRACT TRUNCATED AT 250 WORDS)
Stevenson
B R
BR
Department of Anatomy and Cell Biology, University of Alberta, Edmonton, Canada.
Begg
D A
DA
D000199:Actins / Q000187:drug effects*; D000818:Animals; D002118:Calcium / Q000378:metabolism; D002460:Cell Line; D002463:Cell Membrane Permeability / Q000187:drug effects; D015638:Cytochalasin D / Q000494:pharmacology*; D004285:Dogs; D004351:Drug Resistance; D004847:Epithelial Cells; D017629:Gap Junctions / Q000187:drug effects*; D008853:Microscopy
D000199:Actins; D015638:Cytochalasin D; D002118:Calcium