Glucose transport and equilibrium across alveolar-airway barrier of rat.
The glucose concentration in the epithelial lining fluid (ELF) results from a balance between cellular uptake and paracellular leakage. The present study examines whether the ELF glucose concentration can be predicted from the kinetics of glucose transport obtained in fluid-filled lungs. Isolated rat lungs were filled via the trachea with instillate containing 0-10 mM glucose; the perfusate glucose concentration was 10 mM. The rate of glucose removal from airspaces depended on luminal glucose concentration and was saturable [maximum uptake rate = 101 +/- 8.6 mumol.h-1.g dry lung wt-1; apparent Michaelis constant K(m) = 1.5 +/- 0.43 mM; R2 = 0.79]. Glucose removal was inhibited by phloridzin but not by phloretin or by inhibiting glycolysis. The steady-state concentration in fluid-filled lungs was estimated to be 0.15 +/- 0.034 mM. It agreed with that (< 1/20 plasma) calculated using glucose transport kinetics and paracellular permeability. The ELF glucose concentration obtained by bronchoalveolar lavage was 0.39 +/- 0.012 plasma in vivo and 0.39 +/- 0.021 perfusate in air-filled isolated lungs. The equilibrium ELF/perfusate distribution ratio of alpha-methyl-glucose was similar to that of glucose. Thus there is a major difference between the alveolar steady-state glucose concentration in air- and fluid-filled lungs despite similar mechanisms of airspace glucose removal. This suggests that glucose kinetics or access to uptake sites differ in air- and fluid-filled lungs.
Saumon
G
G
Institut National de la Santé et de la Recherche Médicale U82, Faculté Xavier Bichat, Paris, France.
Martet
G
G
Loiseau
P
P
D000388:Air; D000818:Animals; D001692:Biological Transport; D015824:Blood-Air Barrier; D001992:Bronchoalveolar Lavage Fluid / Q000737:chemistry; D005947:Glucose / Q000493:pharmacokinetics*; D066298:In Vitro Techniques; D008168:Lung / Q000502:physiology; D051381:Rats; D017208:Rats, Wistar; D012996:Solutions
D012996:Solutions; D005947:Glucose