Biochemical evidence for transcytotic absorption of polyaspartamide from the rat lung: Effects of temperature and metabolic inhibitors

Airway‐to‐perfusate polyhydroxyethylaspartamide (PHEA) absorption was studied in the isolated perfused rat lung at a reduced temperature and by the use of metabolic inhibitors, to kinetically clarify the mechanisms and cellular pathways of its active absorption. Fluorophore‐labeled PHEA (F‐PHEA; 7.4 kDa) was administered into the airways, and its absorption followed with time at 25°C and in the presence of 2,4‐dinitrophenol (DNP), ouabain (OUA), monensin (MON), and nocodazole (NOC). Across‐dose absorption profiles were analyzed using a kinetic model incorporating active (Vmax,P and Km,P) and passive (ka,P) absorption from the pulmonary lung region alongside the competing, pulmonary‐to‐bronchial mucociliary escalator (kE). The model was validated at 25°C and a lack of perturbation on the ka,P and kE values for passively absorbed solutes confirmed by studying the disposition of sodium fluorescein and 4.4 kDa fluorescein isothiocyanate‐labeled dextran. F‐PHEA absorption was significantly suppressed at 25°C, compared with 37°C, because of a significant decrease in the value of the maximum rate of active absorption, Vmax,P (4.37 → 0.67 μg/min; p