Characteristics of Passive Solute Transport across Primary Rat Alveolar Epithelial Cell Monolayers

Abstract

Primary rat alveolar epithelial cell monolayers (RAECM) were grown without (type I cell-like phenotype, RAECM-I) or with (type II cell-like phenotype, RAECM-II) keratinocyte growth factor to assess passive transport of 11 hydrophilic solutes. We estimated apparent permeability (Papp) in the absence/presence of calcium chelator EGTA to determine the effects of perturbing tight junctions on “equivalent” pores. Papp across RAECM-I and -II in the absence of EGTA are similar and decrease as solute size increases. We modeled Papp of the hydrophilic solutes across RAECM-I/-II as taking place via heterogeneous populations of equivalent pores comprised of small (0.41/0.32 nm radius) and large (9.88/11.56 nm radius) pores, respectively. Total equivalent pore area is dominated by small equivalent pores (99.92–99.97%). The number of small and large equivalent pores in RAECM-I was 8.55 and 1.29 times greater, respectively, than those in RAECM-II. With EGTA, the large pore radius in RAECM-I/-II increased by 1.58/4.34 times and the small equivalent pore radius increased by 1.84/1.90 times, respectively. These results indicate that passive diffusion of hydrophilic solutes across an alveolar epithelium occurs via small and large equivalent pores, reflecting interactions of transmembrane proteins expressed in intercellular tight junctions of alveolar epithelial cells.

Organic Anion Detection with Functionalized SERS Substrates via Coupled Electrokinetic Preconcentration, Analyte Capture, and Charge Transfer

“…For proof-of-concept and to identify a suitable range of applied potentials, SERS was conducted with 1 μM 5(6)-FAM using CA-SAM substrates and peak intensities were recorded over time with potentials ranging from +100 to +500 mV corresponding to electric field strengths ( E = V ( dK ) −1 where K = εε 0 is the dielectric constant for water) of approximately 36–179 V m –1 . At these field strengths, the calculated limiting velocity ( v ) range for 5(6)-FAM is 0.6–3.1 μm s –1 based on Stokes Law, v = z e E (6πη r ) −1 , where z is the number of charges (1 at pH 7), e is the elemental electron charge, η is viscosity (1 mPa·s for water at 20 °C), and r is the Stokes radius (0.49 nm) based on the estimated diffusion coefficient, D , for 5-FAM (4.2 × 10 –10 m 2 s –1 ) . Setting the characteristic length, L , equal to the mean gap between the electrodes, the Peclet number ( Pe L = LvD –1 ) ranged from 4.2 to 20.7.…”

Physiologically Based Modelling Framework for Prediction of Pulmonary Pharmacokinetics of Antimicrobial Target Site Concentrations

“…The alveolar capillary wall is a highly permeable structure [ 24 ], and therefore the full paracellular space was assumed to be available for transport. Paracellular transport over the alveolar epithelium is restricted by tight junctions [ 24 , 25 ], and was assumed to only take place through aqueous pores present in tight junctions. The pore population consisted of two subpopulations, one small ( r s 0.32 nm radius) and one large ( r l 11.52 nm radius), making up 0.303% and 0.00079% of the total alveolar surface area, respectively [ 25 ].…”

“…Paracellular transport over the alveolar epithelium is restricted by tight junctions [ 24 , 25 ], and was assumed to only take place through aqueous pores present in tight junctions. The pore population consisted of two subpopulations, one small ( r s 0.32 nm radius) and one large ( r l 11.52 nm radius), making up 0.303% and 0.00079% of the total alveolar surface area, respectively [ 25 ]. Passage through the pores was assumed possible for molecules with radius r smaller than the pore radius ( r s or r l ).…”

“…The molecular radius r was assumed to be constant and calculated according to the Stoke–Einstein equation (Eq. 8 ) [ 25 , 27 ]. where k is the Boltzmann constant (1.38*10 −23 J/K), T is the absolute body temperature (309.95 K) and η is the viscosity of water at 309.95 K (0.69 mPa × s) [ 28 ].…”

Clearance of nanoparticles from blood: effects of hydrodynamic size and surface coatings

“…Pores of the interendothelial cell junction openings for non-fenestrated blood capillaries in lungs, skin and intestinal mesentery have sizes of approximately 5 nm. 30 NP penetration to the kidney also facilitates their clearance from blood. The glomerular epithelial (fenestrated) filtration slit is 12.1-15 nm in general, 31,32 and 5.5 nm (ref.…”