title: Mechanism and size cutoff for steric exclusion from actin-rich cytoplasmic domains.
abstract: Subdomains of the cytoplasmic volume in tissue culture cells exclude large tracer particles relative to small. Evidence suggests that exclusion of the large particles is due to molecular sieving by the dense meshwork of microfilaments found in these compartments, but exclusion as a result of the close apposition of the dorsal and ventral plasma membrane of the cell in these regions has not been ruled out conclusively. In principle, these two mechanisms can be distinguished by the dependence of exclusion on tracer particle size. By fluorescence ratio imaging we have measured the partition coefficient (P/PO) into excluding compartments for tracer particles ranging in radius from 1 to 41 nm. The decay of P/PO as a function of particle radius is better fitted by three molecular sieving models than by a slit pore model. The sieving models predict a percolation cutoff radius of the order of 50 nm for partitioning into excluding compartments.
authors.affiliation: University of Texas Southwestern Medical Center at Dallas 75235-9040, USA.
authors.forename: L W
authors.initials: LW
authors.lastname: Janson
authors.forename: K
authors.initials: K
authors.lastname: Ragsdale
authors.forename: K
authors.initials: K
authors.lastname: Luby-Phelps
mesh_terms: D016475:3T3 Cells; D000199:Actins / Q000737:chemistry* / Q000378:metabolism*; D000818:Animals; D055592:Biophysical Phenomena; D001703:Biophysics; D002232:Carbocyanines; D002451:Cell Compartmentation; D003593:Cytoplasm / Q000378:metabolism*; D005362:Ficoll / Q000031:analogs & derivatives; D016650:Fluorescein-5-isothiocyanate / Q000031:analogs & derivatives; D005456:Fluorescent Dyes; D051379:Mice; D008856:Microscopy, Fluorescence; D008954:Models, Biological; D010316:Particle Size; D012235:Rhodamines
chemical_list: D000199:Actins; D002232:Carbocyanines; D005456:Fluorescent Dyes; D012235:Rhodamines; C085321:cyanine dye 5; C045540:fluorescein 5-isothiocyanate-Ficoll; D005362:Ficoll; D016650:Fluorescein-5-isothiocyanate