Two-channel transporter versus a single-channel Na+-dependent transporter for glucose and amino acids in rat and...

Conditions in rat and turtle small intestine tissue where glucose and glycine transport are inhibited while glucose-induced Na+ transport is preserved are described. The generally accepted model for the Na(+)-dependent transporter (a single channel for the Na+ and nutrient) does not account for the data obtained from an analysis of the interaction between the transport of glucose, glycine, and Na+ at different temperatures and the effect of inhibitors on these processes. The phenomenon of uncoupling of Na+ and nutrient transport can best be described by a two-channel model with a gate mechanism. According to this model, the Na(+)-dependent transporter has at least two channels: one for Na+ and another for nutrients. The model provides for the passage of Na+ in both directions along a channel opened by glucose, and accounts for changes in the stoichiometric ratio of Na+: glucose transport. Experiments are reported that confirm these theoretical predictions.