Fig. 8.  Paracellular diffusion drives airway surface liquid (ASL) glucose concentration. A and B: transepithelial electrical resistance (TEER, A) and glucose concentration (B) in ASL washes after exposure to 5 mM glucose (●) or 15 mM glucose (▲) and 3-bromopyruvic acid (BrPy; ○ or ▽, respectively). Individual data points are shown with mean ± SD; n = 6 experiments. ****P < 0.0001. C and D: proposed mechanism for the role of hexokinase II (HKII) in maintaining low intracellular glucose in normoglycemia (C) and hyperglycemia (D). There is a diffusion gradient for paracellular movement of glucose from the blood/interstitium to the ASL. Glucose uptake via glucose transporters (GLUTs) is maintained by metabolism, which generates low intracellular glucose. We propose that this occurs predominantly by HKII-driven conversion of glucose to glucose-6-phosphate (G-6-P) and glycolysis. When blood glucose levels are raised to 15 mM (hyperglycemia), there is increased paracellular movement of glucose into the ASL. Increased glucose uptake elevates HKII activity at the mitochondria, increasing G-6-P, glycolysis, and glycogen synthesis. This effectively reduces intracellular glucose concentration, which maintains a glucose gradient for clearance of glucose from the ASL and prevents transcellular efflux into the ASL. Inhibition of HKII with BrPy elevates intracellular glucose, but concentrations remain low compared with external glucose concentration indicating additional contribution of HKI/III and the HK-independent polyol pathway to glucose metabolism. MCTs, monocarboxylate lactate-H+ cotransporters; TCA, tricarboxylic acid cycle.