Meeting future challenges in topical ocular drug delivery: Development of an air-interfaced primary culture of rabbit conjunctival epithelial cells on a permeable support for drug transport studies

The purpose of this study was to develop and characterize a functional air-interfaced primary culture of rabbit conjunctival epithelial cells gl awn on a permeable support for drug transport studies. Cunjunctival epithelial cells from the pigmented rabbit were isolated, seeded at 1.2x10(6) cells cm(-2) on permeable Transwell filters, and cultured at the air interface using a modified PC-1 medium. Conjunctival epithelial cell layers showed a transepithelial resistance of 1.1+/-0.1 k Omega cm(2), a potential difference of 17.0+/-0.5 mV, and an equivalent short-circuit current (I-eq) of 16. 1+/-0.4 mu A cm(-2). The I-eq was reduced by 35% using 0.01 mM bumetanide, 66% using 0.1 mM ouabain, 46% using 2 mM barium chloride (all three in the basolateral fluid), and 63% using 0.3 mM NPAA in the apical fluid, consistent with active C1(-)-secretion across the conjunctival epithelial barrier. Amiloride-sensitive Na- channels were absent. The permeability of the cell layers to polar solutes decreased with increased solute size, and the calculated equivalent pole size was about 8.0 nm. The Papp of beta-blockers varied with lipophilicity in a sigmoidal fashion. Uridine transport showed temperature sensitivity and directionality, favoring transport in the apical-to-basolateral direction. Apical L-carnosine uptake was reduced by 46% in the absence of an inwardly directed proton gradient, and lowering the temperature to 4 degrees C abolished direction-dependent L-carnosine uptake. Furthermore, uptake was inhibited by 73% using apical 10 mM glycyl sarcosine (a dipeptide transporter substrate) and by 60% using 1 mM L-valacyclovir (a dipeptide prodrug). In conclusion, a functional air-interfaced primary culture of rabbit conjunctival epithelial cell layers was established. This air-interfaced primary culture model may be useful for studying passive and active transport processes for ion and solute translocation in the mammalian conjunctival epithelial barrier in a defined experimental setting. (C) 2000 Elsevier Science B.V. All right reserved.