Choline transport by lung epithelium.
The uptake of [3H]choline was investigated using isolated perfused rat lungs and primary cultures of granular pneumocytes isolated by tryptic digestion of rat lungs. Metabolic products were separated from free choline by chloroform:methanol extraction and column chromatography. Tissue-associated [3H]choline increased progressively in the perfused lung, and estimated mean intracellular concentration at 2 h was 12 times the extracellular concentration (5 microM). Choline uptake was inhibited by ventilation with CO and by perfusion with the choline analog, hemicholinium-3 (HC-3). Isolated granular pneumocytes also accumulated choline against a concentration gradient by an energy-dependent process. The concentration for half-maximal uptake, after correction for the diffusion component, was estimated at 18 +/- 4 microM (mean +/- SE; n = 3), and the estimated maximal rate of uptake was 213 +/- 44 pmol/min/microliter cell water. HC-3 inhibited uptake by approximately 50% at a concentration of 10(-4) M. There was no effect on uptake when Na+ in the medium was replaced by Li+ or N-methylglucamine+. These results indicate that granular pneumocytes possess a transport system that results in accumulation of choline against a concentration gradient. The characteristics of uptake indicate that this system is similar to the low affinity choline transport system of other organs.
Fisher
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AB
Institute for Environmental Medicine, University of Pennsylvania School of Medicine, Philadelphia 19104-6068.
Chander
A
A
Dodia
C
C
Reicherter
J
J
Kleinzeller
A
A
D000818:Animals; D001693:Biological Transport, Active / Q000187:drug effects; D002478:Cells, Cultured; D002794:Choline / Q000378:metabolism*; D004848:Epithelium / Q000378:metabolism; D006426:Hemicholinium 3 / Q000494:pharmacology; D007700:Kinetics; D008168:Lung / Q000166:cytology / Q000378:metabolism*; D008297:Male; D010477:Perfusion; D051381:Rats; D011919:Rats, Inbred Strains; D012964:Sodium / Q000378:metabolism; D013696:Temperature
D006426:Hemicholinium 3; D012964:Sodium; D002794:Choline