title: Pantothenate-sodium cotransport in renal brush-border membranes.
abstract: The mechanism of pantothenate transport into rabbit renal brush-border membrane vesicles was studied. Under voltage-clamped conditions, an inward NaCl gradient induced the transient accumulation of pantothenate against its concentration gradient, indicating Na+/pantothenate cotransport. K+, Rb+, Li+, NH4+, and choline+ were ineffective in replacing Na+. Pantothenate analogs, D-glucose, and various carboxylic acids did not inhibit Na+-dependent pantothenate transport, suggesting that this system is specific for pantothenate. Kinetic analysis of the Na+-dependent pantothenate uptake revealed a single transport system which obeyed Michaelis-Menten kinetics (Km = 16 microM and Vmax = 6.7 pmol X mg-1 X 10 s-1). Imposition of an inside-negative membrane potential caused net uphill pantothenate accumulation in the presence of Na+ but absence of a Na+ gradient, indicating that Na+/pantothenate cotransport is electrogenic. The relationship between extravesicular Na+ concentration and pantothenate transport measured under voltage-clamped conditions was sigmoidal: a Hill coefficient (napp) of 2 and a [Na+]0.5 of 55 mM were calculated. It is suggested that an anionic pantothenate1- molecule is cotransported with two Na+ to give a net charge of +1. The coupling of pantothenate transport to the Na+ electrochemical gradient may provide an efficient mechanism for reabsorption of pantothenate in the kidney.
mesh_terms: D000818:Animals; D002414:Cations, Monovalent; D007672:Kidney Cortex / Q000378:metabolism*; D007700:Kinetics; D008871:Microvilli / Q000378:metabolism*; D009994:Osmolar Concentration; D010205:Pantothenic Acid / Q000031:analogs & derivatives / Q000378:metabolism* / Q000494:pharmacology; D011817:Rabbits; D012964:Sodium / Q000378:metabolism*
chemical_list: D002414:Cations, Monovalent; D010205:Pantothenic Acid; D012964:Sodium