Question

Cholera toxin inhibits the Na+/K+ATPase activity of intestinal epithelial cells. Resulting with decreased uptake of glucose. Describe why inhibiting the Na/K+ ATPase pump affects glucose uptake in the intestine.

Answer 1

Na+/K+-ATPase  is an enzyme found in the plasma membrane of all animal cells. The Na+/K+-ATPase enzyme is a solute pump that pumps sodium out of cells while pumping potassium into cells, both against their concentration gradients. It has antiporter-like activity, but since it moves both molecules against their concentration gradients it is not a true antiporter, which would require one solute to move with its gradient, not against it. Its simple function is to pump 3 sodium ions out for every 2 potassium ions taken in and since they both have equal ionic charges, this creates an electrochemical gradient between a cell and its exterior.

In small intestine, glucose is actively transported against its chemical gradient into the epithelial enterocytes by cotransport of sodium by means of transporters such as GLUT4. The sodium concentration inside the enterocyte ([Nac]) is kept low by basolateral Na-K-ATPase, which cleaves ATP to transport sodium ions against their concentration gradient out of the cell and potassium ions against their gradient into the cell. In the gut, sodium is transported out of the reabsorbing cell on the blood (interstitial fluid) side via the Na+-K+ pump, whereas, on the reabsorbing (lumenal) side, the Na+-glucose symporter uses the created Na+ gradient as a source of energy to import both Na+ and glucose, which is far more efficient than simple diffusion.

Inhibition of Na/K+ ATPase pump will lead to increase in concentration of Na+ on the inside of cell, which will inhibit the Na+/Glucose symporter from transporting the sodium inside the cell along with glucose thus resulting in a decreased uptake of glucose.