Unidirectional uptake of substrates at the blood side of secretory epithelia: stomach, salivary gland, pancreas.
This paper reviews studies of cellular uptake of substrates by the gastric mucosa, salivary gland, and pancreas by single-circulation, multiple tracer dilution techniques. The application of this methodology to secretory organs in vivo has permitted the characterization of transport phenomena at the blood-tissue interface of resting and secreting epithelia. To estimate uptake of a test molecule after an intraarterial injection, its venous concentration profile (30 samples in 1 in) was compared with that of 1) an intravascular marker or 2) a diffusible molecule that remains confined to the extracellular space. Among the molecules investigated were 86Rb, 57Co-labeled cyanocobalamin, 125I-labeled insulin, [3H]ouabain, [3H]dopamine, [3H]norepinephrine, and a wide range of labeled amino acids. High tracer uptake (80%) was measured that could be inhibited by specific unlabeled competitors. Unidirectional influx was saturable and Michaelis-Menten kinetic constants could be estimated. The ultimate objective was to identify various transport systems and/or receptors at the basolateral side of these epithelia. However, nerve terminals in the interstitium could be the major site for the uptake of catecholamines.
D000596:Amino Acids / Q000378:metabolism; D000818:Animals; D001692:Biological Transport; D002395:Catecholamines / Q000378:metabolism; D002415:Cats; D004848:Epithelium / Q000378:metabolism; D005753:Gastric Mucosa / Q000378:metabolism*; D007201:Indicator Dilution Techniques; D007328:Insulin / Q000378:metabolism; D007477:Ions; D008657:Metabolic Clearance Rate; D010042:Ouabain / Q000378:metabolism; D010179:Pancreas / Q000378:metabolism*; D012039:Regional Blood Flow; D012469:Salivary Glands / Q000378:metabolism*; D014805:Vitamin B 12 / Q000378:metabolism
D000596:Amino Acids; D002395:Catecholamines; D007328:Insulin; D007477:Ions; D010042:Ouabain; D014805:Vitamin B 12