Electrogenic Na(+)-dependent L-alanine transport in the lizard duodenum. Involvement of systems A and ASC.
L-Alanine transport across the isolated duodenal mucosa of the lizard Gallotia galloti has been studied in Ussing chambers under short-circuit conditions. Net L-alanine fluxes, transepithelial potential difference (PD), and short-circuit current (Isc) showed concentration-dependent relationships. Na(+)-dependent L-alanine transport was substantially inhibited by the analog alpha-methyl aminoisobutyric acid (MeAIB). Likewise, MeAIB fluxes were completely inhibited by L-alanine, indicating the presence of system A for neutral amino acid transport. System A transport activity was electrogenic and exhibited hyperbolic relationships for net MeAIB fluxes, PD, and Isc, which displayed similar apparent K(m) values. Na(+)-dependent L-alanine transport, but not MeAIB transport, was partially inhibited by L-serine and L-cysteine, indicating the participation of system ASC. This transport activity represents the major pathway for L-alanine absorption and seemed to operate in an electroneutral mode with a negligible contribution to the L-alanine-induced electrogenicity. It is concluded from the present study that the active Na(+)-dependent L-alanine transport across the isolated duodenal mucosa of Gallotia galloti results from the independent activity of systems A and ASC for neutral amino acid transport.
Medina
V
V
Laboratorio de Fisiología Animal, Departamento de Biología Animal, Universidad de La Laguna, 38206 Tenerife, Spain.
Lorenzo
A
A
Díaz
M
M
D000409:Alanine / Q000378:metabolism* / Q000494:pharmacology; D000818:Animals; D001692:Biological Transport / Q000187:drug effects; D002352:Carrier Proteins / Q000378:metabolism*; D003545:Cysteine / Q000494:pharmacology; D004386:Duodenum / Q000378:metabolism*; D004553:Electric Conductivity; D004848:Epithelium / Q000502:physiology; D007413:Intestinal Mucosa / Q000378:metabolism; D007700:Kinetics; D008116:Lizards / Q000378:metabolism*; D008564:Membrane Potentials / Q000187:drug effects; D012694:Serine / Q000494:pharmacology; D012964:Sodium / Q000494:pharmacology*; D015091:beta-Alanine / Q000031:analogs & derivatives* / Q000378:metabolism / Q000494:pharmacology
D002352:Carrier Proteins; D015091:beta-Alanine; C012924:2,2-dimethyl-beta-alanine; D012694:Serine; D012964:Sodium; D003545:Cysteine; D000409:Alanine