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Abstract

Transport of 14C-labeled acetic, propionic (PA), butyric, valeric, heptanoic (HA), and octanoic (OA) acids across the Madin Darby canine kidney (MDCK) epithelial cell monolayer grown on a porous polycarbonate membrane was studied in Hanks' balanced salt solution (HBSS) at 37 degrees C in both apical-to-basolateral and basolateral-to-apical directions. At micromolar concentrations of solutes, metabolic decomposition was significant as evidenced by [14C]CO2 production during the OA transport. The apparent permeability (Pe) indicates that as lipophilicity increases, diffusion across the "unstirred" boundary layer becomes rate limiting. In support of this notion, transport of OA and HA was enhanced by agitation, showed an activation energy of 3.7 kcal/mol for OA, and resulted in identical Pe values for both transport directions. Analysis of Pe changes with varying alkyl chain length resulted in a delta G of -0.68 +/- 0.09 kcal/mol for -CH2-group transfer from an aqueous phase to the MDCK cells. When the intercellular tight junctions were opened by the divalent chelator EGTA in Ca2+/Mg2(+)-free HBSS, transport of the fluid-phase marker Lucifer yellow greatly increased because of paracellular leakage. PA transport also showed a significant increase, but OA transport was independent of EGTA. Although albumin also undergoes paracellular transport in the presence of EGTA and OA binds strongly to albumin, OA transport in EGTA solution was unchanged by albumin. These observations indicate that transmembrane transport is the major mechanism for lipophilic substances. The present study, together with earlier work on the transport of polar substances, shows that the MDCK cell monolayer is an excellent model of the transepithelial transport barrier.

Cosmic‐Ray Scattering and Streaming in Compressible Magnetohydrodynamic Turbulence

“…For a present numerical studies this is extremely challenging, however. Nevertheless, the correspondence of properties of MHD turbulence with and without mean magnetic field reported in Cho & Lazarian (2003b) supports the theoretical expectations about the modes. One way or another, there are theoretical expec-tations that have been tested for the case most important for scattering of Galactic cosmic rays.…”

Transepithelial Transport and Metabolism of Boronated DipeptidesAcross Caco‐2 and HCT‐8 Cell Monolayers

“…It 13oo (1-e) The apparent permeability coefficient (Pe) can be calculated from the slope of a plot of the mass transported divided by the product of the Transvell (R) surface area (4.71 cm2) and the initial concentration versus time (14). Alternatively, Pe can be calculated from the derivative of the first order equation at time…”

“…The Caco-2 cell line was obtained from the Lineberger Cancer Center at the University of North Carolina at Chapel Hill at different serial passage numbers (13)(14)(15)(16). For the transport studies, cells were diluted with growth medium to give a total of 7.5 x 10 cells/cm in 1.5 mls.…”

“…The monolayer integrity was tested both before and after transport experiments by monitoring the passage of the fluid-phase marker Lucifer yellow CH from the apical to the basal compartment. The integrity was further tested by measuring the potential difference across the monolayer using a transepithelial electrical resistance device described elsewhere (14) in which 50 A of current is applied across the monolayer and the electrical resistance across tight junctions is determined from Ohm's Law in units of f) cm2. After completing the transport experiments, the monolayers were immersed in a 37% formaldehyde solution for 30 minutes.…”