Question

What effect will the following mutations have on intestinal epithelial transport? Consider all the players that are being transported (water, Na+, glucose, K+)
a.  a mutation that inhibits the Na+/K+ ATPase
b.  a mutation that blocks binding of the glucose to the glucose transporter on the basolateral membrane

Answer 1

Na- K ATPase is located on the lateral surface of epithelial cell. This is a type of primary active transport , it utilizes ATP and tranport Na out side of cell ( in the lumen ) and K in the epithelial cell. By doing so it maintain high concentration gradient of Na across the intestinal lumen. This Na gradient is actually use for absorption of various molecules like glucose and amino acid etc.

A) if there is a mutation in Na - K ATPase , then concentration gradient of Na will not form and glucose will not absorb. Here K concentration will be higher in the intestinal lumen and Na will be higher in intestinal cell.

Movement of water in the the intestine follow movement of other constituents to maintain osmotic equilibrium. So water absorption will also stop.

2) once glucose absorbed using Na Glut transporter, in SIDS the intestinal cell GLUT- 2 transporter is present on basolateral membrane . This transport glucose in to the blood vessels by a process facilitated diffusion. In case of mutation glucose is not absorbed in to the blood and there will be increased concentration of glucose in intestinal cell.

As glucose is not transported by GLUT 2, glucose absorption from intestine by Na- GLUT receptor will also stop. And this will further stop functioning of Na- K ATPase .

For better understanding the transport of molecules has be shown in attached image below