11. Biological Membranes and Transport

The Na⁺-Glucose symporter transports the two molecules into the cell, while the Na⁺-K⁺ ATPase uses ATP to transport Na+ ions out of the cell. What would be the result of a mutation leading to a nonfunctional Na⁺-Glucose symporter?

Imagine that you perform a series of experiments to test the rate of glucose transport (V₀) into epithelial cells using the Na⁺-Glucose symporters. These experimental epithelial cells contain no intracellular Na⁺ but have the same glucose concentration as their surroundings. In experiment #1, you transfer your cells to test tubes that contain different extracellular [Na⁺] & then measure the rate of glucose transport (V₀). In experiment #2, you introduce leakage Na+ channels into the cell membranes & then repeat the same experiment. Label the data on the plot below as showing results to either Experiment #1 or Experiment #2.