Kinetics of the Na+/alanine cotransporter in pancreatic acinar cells.
Electric currents associated with Na+-coupled alanine transport in pancreatic acinar cells were investigated by the technique of tight-seal whole-cell recordings. In a previous study the observed concentration dependence of alanine-dependent currents was found to be consistent with a 'simultaneous' transport mechanism with 1:1 stoichiometry. In the present work the sidedness of the cotransporter was investigated by comparing inward (I") and outward currents (I') measured under mirror-symmetrical conditions. I' and I" were found to be nearly equal (within a factor of approx. 2) in a wide range of Na+ and alanine concentrations. The transport model was further tested by 'infinite-cis' experiments with fixed, saturating concentrations of Na+ and L-alanine on one side of the membrane and variable concentrations on the other. By measuring transmembrane currents as a function of Na+ and alanine concentrations, numerical values of the equilibrium dissociation constants of both substrates could be estimated.
Jauch
P
P
Department of Biology, University of Konstanz, F.R.G.
Läuger
P
P
D000409:Alanine / Q000378:metabolism / Q000494:pharmacology; D026905:Amino Acid Transport Systems; D026921:Amino Acid Transport Systems, Neutral; D000818:Animals; D001692:Biological Transport; D002352:Carrier Proteins / Q000378:metabolism*; D002462:Cell Membrane / Q000378:metabolism; D003593:Cytoplasm / Q000378:metabolism; D004553:Electric Conductivity; D007700:Kinetics; D051379:Mice; D010179:Pancreas / Q000378:metabolism*; D012964:Sodium / Q000378:metabolism / Q000494:pharmacology; D027981:Symporters
D026905:Amino Acid Transport Systems; D026921:Amino Acid Transport Systems, Neutral; D002352:Carrier Proteins; D027981:Symporters; C052168:sodium-alanine cotransporter; D012964:Sodium; D000409:Alanine