title: Membrane mechanisms for electrogenic Na(+)-independent L-alanine transport in the lizard duodenal mucosa.
abstract: The active Na(+)-independent transport of L-alanine across the duodenal mucosa of the lizard Gallotia galloti was studied in Ussing-type chambers using a computer-controlled voltage clamp. Addition of L-alanine to the Na(+)-free bathing solutions resulted in a significant L-alanine absorption (J(net)) that was paralleled by an increase in transepithelial short-circuit current (I(sc)) and potential difference (PD) without apparent changes in the tissue conductance. The concentration dependence of J(net), PD, and I(sc) displayed Michaelis-Menten kinetics. L-alanine-induced electrical changes were completely inhibited by external alkaline pH or by the H(+)-ionophore carbonyl cyanide m-chlorophenyl-hydrazone in the bathing solution. The alanine-induced electrogenicity was dependent on the presence of extracellular K(+) and could be blocked by serosal Ba(2+) or mucosal orthovanadate. These results suggest the existence of an H(+)-coupled L-alanine cotransport at the apical membrane of enterocytes. The favorable H(+) driving force is likely to be maintained by an apical vanadate-sensitive H(+)-K(+)-ATPase, allowing the extrusion of H(+) in an exchange with K(+). Potassium exit through a basolateral barium-sensitive conductance provides the key step for the electrogenicity of L-alanine absorption.
authors.affiliation: Laboratorio de Fisiología Animal, Departamento de Biología Animal, Universidad de La Laguna, 38206 Tenerife, Spain. madiaz@ull.es
authors.forename: M
authors.initials: M
authors.lastname: Díaz
authors.forename: V
authors.initials: V
authors.lastname: Medina
authors.forename: T
authors.initials: T
authors.lastname: Gómez
authors.forename: A
authors.initials: A
authors.lastname: Lorenzo
mesh_terms: D000409:Alanine / Q000493:pharmacokinetics*; D026905:Amino Acid Transport Systems; D000596:Amino Acids / Q000494:pharmacology; D000598:Amino Acids, Cyclic; D000818:Animals; D002352:Carrier Proteins / Q000378:metabolism*; D003515:Cycloleucine / Q000494:pharmacology; D004386:Duodenum / Q000378:metabolism*; D004791:Enzyme Inhibitors / Q000494:pharmacology; D005033:Ethylmaleimide / Q000494:pharmacology; D005260:Female; D017506:H(+)-K(+)-Exchanging ATPase / Q000378:metabolism; D006863:Hydrogen-Ion Concentration; D007408:Intestinal Absorption / Q000187:drug effects / Q000502:physiology*; D007413:Intestinal Mucosa / Q000201:enzymology; D007700:Kinetics; D008116:Lizards / Q000378:metabolism*; D008297:Male; D008564:Membrane Potentials / Q000187:drug effects / Q000502:physiology; D018408:Patch-Clamp Techniques; D011522:Protons; D012694:Serine / Q000493:pharmacokinetics; D012964:Sodium / Q000378:metabolism; D014638:Vanadates / Q000494:pharmacology
chemical_list: D026905:Amino Acid Transport Systems; D000596:Amino Acids; D000598:Amino Acids, Cyclic; D002352:Carrier Proteins; D004791:Enzyme Inhibitors; D011522:Protons; D003515:Cycloleucine; C006504:2-aminobicyclo(2,2,1)heptane-2-carboxylic acid; D014638:Vanadates; D012694:Serine; D012964:Sodium; D017506:H(+)-K(+)-Exchanging ATPase; D005033:Ethylmaleimide; D000409:Alanine