Rates of Protein Transport Across Rat Alveolar Epithelial Cell Monolayers

Yasuhisa Matsukawa Department of Pharmaceutical Sciences, University of Southern California, Los Angeles, CA, 90033, USA

Hiroshi Yamahara Department of Pharmaceutical Sciences, University of Southern California, Los Angeles, CA, 90033, USA

Fumiyoshi Yamashita Department of Pharmaceutical Sciences, University of Southern California, Los Angeles, CA, 90033, USA

Vincent H.L. Lee Department of Pharmaceutical Sciences, University of Southern California, Los Angeles, CA, 90033, USA; Department of Ophthalmology, University of Southern California, Los Angeles, CA, 90033, USA

Edward D. Crandall Department of Ophthalmology, University of Southern California, Los Angeles, CA, 90033, USA; Department of Pathology, University of Southern California, Los Angeles, CA, 90033, USA; Will Rogers Institute Pulmonary Research Center, University of Southern California, Los Angeles, CA, 90033, USA

Kwang-Jin Kim Department of Medicine, University of Southern California, Los Angeles, CA, 90033, USA; Department of Physiology and Biophysics, University of Southern California, Los Angeles, CA, 90033, USA; Department of Biomedical Engineering, University of Southern California, Los Angeles, CA, 90033, USA; Department of Molecular Pharmacology and Toxicology, University of Southern California, Los Angeles, CA, 90033, USA; Will Rogers Institute Pulmonary Research Center, University of Southern California, Los Angeles, CA, 90033, USA

Abstract

The transport of model proteins, ranging from 12, 300 to 150, 000 Da, across tight rat alveolar epithelial cell monolayers (>2000 cm²) grown on polycarbonate filters, was studied. Model proteins were ¹⁴C-cytochromec, ¹⁴C-ovalbumin, granulocyte-colony stimulating factor (G-CSF), ¹⁴C-bovine serum albumin (BSA), ¹²⁵I-transferrin, and ¹⁴C-immunoglobulin G. Cytochrome c was extensively metabolized, as indicated by < 10% of the dose being translocated in intact form. This contrasts with 20–80% for the other model proteins studied. The flux of cytochrome c and G-CSF was symmetric in the apical-to-basolateral (ab) and basolateral-to-apical (ba) directions. By contrast, the flux of intact ovalbumin, BSA, transferrin and immunoglobulin G showed asymmetry, with the ab flux being higher by 2-5 times. There was no relationship between ab or ba fluxes and the molecular weights of these four model proteins. Since some of the proteins were translocated at much greater rates than are consistent with restricted diffusion or pinocytosis, receptor-mediated or adsorptive transcytosis may be involved.

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Rates of Protein Transport Across Rat Alveolar Epithelial Cell Monolayers

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Rates of Protein Transport Across Rat Alveolar Epithelial Cell Monolayers

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