Organic cation transport in rabbit alveolar epithelial cell monolayers.
OBJECTIVE
To characterize organic cation (OC) transport in primary cultured rabbit alveolar epithelial cell monolayers, using [14C]-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 precoated 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, tetraethylammonium, and verapamil. Apical guanidine uptake (Km = 129 +/- 41 microM, Vmax = 718 +/- 72 pmol/mg protein/5 min) was kinetically different from basolateral uptake (Km = 580 +/- 125 microM, 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) x 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.
Shen
J
J
Department of Pharmaceutical Sciences, University of Southern California, Los Angeles 90033, USA.
Elbert
K J
KJ
Yamashita
F
F
Lehr
C M
CM
Kim
K J
KJ
Lee
V H
VH
D000818:Animals; D002250:Carbon Radioisotopes; D002412:Cations / Q000378:metabolism*; D002463:Cell Membrane Permeability; D002478:Cells, Cultured; D004847:Epithelial Cells / Q000378:metabolism; D019791:Guanidine / Q000378:metabolism; D017136:Ion Transport; D007700:Kinetics; D008297:Male; D008353:Mannitol / Q000378:metabolism; D011650:Pulmonary Alveoli / Q000166:cytology / Q000378:metabolism*; D011817:Rabbits; D012964:Sodium / Q000378:metabolism; D013696:Temperature
D002250:Carbon Radioisotopes; D002412:Cations; D008353:Mannitol; D012964:Sodium; D019791:Guanidine