The mechanism of pantothenate transport by rat liver parenchymal cells in primary culture.
The mechanism of pantothenate transport across the plasma membrane was investigated with initial velocity studies of [14C]pantothenate uptake and efflux in rat liver parenchymal cells maintained in primary culture. At 116 mM sodium, double-reciprocal plots of the initial velocity of uptake versus [pantothenate] were linear from 0.3 to 36.5 microM pantothenate and gave an apparent Km,pant of 11 +/- 2 microM. The rate of pantothenate uptake at 0 [sodium] was about 14% of the rate at 116 mM sodium, and the reciprocal of the apparent Km,pant was a linear function of [sodium]. Vmax obtained by extrapolation to infinite [pantothenate] was independent of [sodium]. Ouabain, gramicidin D, cyanide, azide, and 2,4-dinitrophenol inhibited uptake, but preloading cells with pantothenate did not. Pantothenate derivatives or carboxylic acids were only weak inhibitors of uptake. Efflux was measured in cells preloaded with [14C]pantothenate. The apparent Km for efflux was 85 +/- 29 microM, and the rate of efflux was unaffected by addition of pantothenate, sodium, ouabain, gramicidin D, or 2,4-dinitrophenol to the external medium. These features are consistent with a mechanism for pantothenate transport in which sodium and pantothenate are cotransported in a 1:1 ratio on a carrier highly specific for pantothenate; sodium decreases the apparent Km for pantothenate, and a sodium-carrier complex forms only on the intracellular side of the membrane.
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D000818:Animals; D001692:Biological Transport; D002462:Cell Membrane / Q000378:metabolism; D002478:Cells, Cultured; D002712:Chlorides / Q000494:pharmacology; D002794:Choline / Q000378:metabolism; D007700:Kinetics; D008094:Lithium / Q000494:pharmacology; D018021:Lithium Chloride; D008099:Liver / Q000378:metabolism*; D008297:Male; D010101:Oxygen Consumption / Q000187:drug effects; D010205:Pantothenic Acid / Q000378:metabolism*; D051381:Rats; D011919:Rats, Inbred Strains; D012965:Sodium Chloride / Q000378:metabolism
D002712:Chlorides; D010205:Pantothenic Acid; D012965:Sodium Chloride; D008094:Lithium; D018021:Lithium Chloride; D002794:Choline