Pharmaceutical Research

, Volume 9, Issue 8, pp 1029-1034

First online:

The Transport Barrier of Epithelia: A Comparative Study on Membrane Permeability and Charge Selectivity in the Rabbit

  • Yongyut RojanasakulAffiliated withSchool of Pharmacy, West Virginia University
  • , Li-Ying WangAffiliated withSchool of Pharmacy, West Virginia University
  • , Meenakshi BhatAffiliated withSchool of Pharmacy, West Virginia University
  • , Douglas D. GloverAffiliated withSchool of Pharmacy, West Virginia University
  • , Carl J. MalangaAffiliated withSchool of Pharmacy, West Virginia University
  • , Joseph K. H. MaAffiliated withSchool of Pharmacy, West Virginia University

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The transport barrier of the epithelia presents one of the major problems limiting the effective use of these tissues as alternate delivery routes for macromolecules such as peptides and proteins. In the present study, two membrane transport properties, namely, the permeability and permselectivity of the shunt pathway, were investigated and compared in various tissues including the nasal, tracheal, bronchial, buccal, rectal, vaginal, corneal, epidermal, duodenal, jejunal, ileal, and colonic epithelia. Membrane permeability was evaluated using a combined method based on electrical conductance and flux measurements of a hydrophilic fluorescent probe, 6-carboxy fluorescein (CF). Membrane permselectivity or the charge discriminating ability of the membrane was evaluated by KCl diffusion potential measurements. The results indicate that all epithelia under investigation possess a relatively high degree of permeation barrier and are highly selective for the absorption of positively charged solutes. Shunt path permeability was found to vary greatly among tissues from different epithelia, whereas membrane charge selectivity was relatively constant in these tissues. A good correlation was observed between membrane electrical conductance and steady-state flux of CF, indicating a paracellular transport of the compound. The rank order of the intrinsic membrane permeability was as follows: intestinal≈ nasal ≥ bronchial ≥ tracheal > vaginal ≥ rectal > corneal > buccal > skin. Membrane permselectivity, expressed as the ratio of transport number (positive over negative), ranges from 1.78 for the buccal to 1.33 for the rectal epithelium. These results suggest that, for effective delivery purposes, permeation enhancing methods, by either increasing tissue permeability or modifying drug-membrane charge selectivity, are generally required. The permeation data also suggest that the respiratory epithelia represent good alternate routes for drug delivery, particularly for those that are orally ineffective, i.e., due to extensive gastrointestinal tract degradation or first-pass metabolism.

epithelial transport permeability permselectivity absorption electrical resistance electrical conductance diffusion potential