Katharina Elbert

Organic Cation Transport in Rabbit Alveolar Epithelial Cell Monolayers

AbstractPurpose. To characterize organic cation (OC) transport in primary cultured rabbit alveolar epithelial cell monolayers, using [l4C]-guanidine as a model substrate. Methods. Type II alveolar epithelial cells from the rabbit lung were isolated by elastase digestion and cultured on permeable filters pre-coated with fibronectin and collagen. Uptake and transport studies of [14C]-guanidine were conducted in cell monolayers of 5 to 6 days in culture. Results. The cultured alveolar epithelial cell monolayers exhibited the characteristics of a tight barrier. [14C]-Guanidine uptake was temperature dependent, saturable, and inhibited by OC compounds such as amiloride, cimetidine, clonidine, procainamide, propranolol, tetraethyl-ammonium, and verapamil. Apical guanidine uptake (Km = 129 ± 41 μM, Vmax = 718 ± 72 pmol/mg protein/5 min) was kinetically different from basolateral uptake (Km = 580 ± 125 (μM, Vmax = 1,600 ± 160 pmol/mg protein/5 min). [14C]-Guanidine transport across the alveolar epithelial cell monolayer in the apical to basolateral direction revealed a permeability coefficient (Papp) of (7.3 ± 0.4) × 10-7 cm/sec, about seven times higher than that for the paracellular marker [14C]-mannitol. Conclusions. Our findings are consistent with the existence of carrier-mediated OC transport in cultured rabbit alveolar epithelial cells.