title: Active lithium transport by rat renal proximal tubule: a micropuncture study.
abstract: We tested the hypothesis that proximal tubular Li+ reabsorption is due to passive transport. Clearances of [14C]inulin (CIn) and Li+ (CLi), proximal transepithelial electrical potential difference (PD), and tubular fluid-to-plasma Li+ concentration ratios [(TF/P)Li] were measured in anesthetized rats before and after induction of osmotic mannitol diuresis. Late proximal (TF/P)Li was measured after acute intravenous LiCl administration and after addition of LiCl to the diet for 2 days. Glomerular filtration rate (CIn) decreased, whereas CNa and CLi increased during osmotic diuresis. Control early proximal PD was -0.6 mV (lumen negative); late proximal PD (PDLP) was 1.1 mV (lumen positive). PDLP decreased by 1.5 mV to -0.4 mV (lumen negative) after mannitol infusion. Late proximal (TF/P)Li was 1.01 after oral Li+, 1.16 after intravenous Li+ (P < 0.01), and 1.00 during osmotic diuresis. It is concluded that proximal Li+ transfer is distinct from that of Na+, closely parallels proximal water transfer, and involves an active transport mechanism independent of the PD. The data suggest that acute elevation of plasma Li+ concentration may activate a delayed Li+ transport pathway in the proximal convoluted tubule.
authors.affiliation: Department of Medical Physiology, Panum Institute, University of Copenhagen, Denmark.
authors.forename: P P
authors.initials: PP
authors.lastname: Leyssac
authors.forename: O
authors.initials: O
authors.lastname: Frederiksen
authors.forename: N H
authors.initials: NH
authors.lastname: Holstein-Rathlou
authors.forename: A C
authors.initials: AC
authors.lastname: Alfrey
authors.forename: P
authors.initials: P
authors.lastname: Christensen
mesh_terms: D000758:Anesthesia; D000818:Animals; D001693:Biological Transport, Active; D004032:Diet; D004231:Diuresis; D004563:Electrochemistry; D006221:Halothane; D007275:Injections, Intravenous; D007687:Kidney Tubules, Proximal / Q000378:metabolism*; D008094:Lithium / Q000008:administration & dosage / Q000493:pharmacokinetics*; D008297:Male; D008353:Mannitol / Q000494:pharmacology; D011677:Punctures; D051381:Rats; D011919:Rats, Inbred Strains; D013874:Thiopental / Q000031:analogs & derivatives
chemical_list: C004316:thiobutabarbital; D008353:Mannitol; D008094:Lithium; D013874:Thiopental; D006221:Halothane