SGLT 1 Symporter

SGLT 1

(in gut epithelia)

By: Billie-Dee Mansfield

General knowledge: SGLT stands for Sodium Glucose Transport. SGLT is known as a symporter since both the Sodium ions and glucose molecules move in the same direction. Note: The word symporter contains the root word "Sym", meaning same. Two sodium ions enter the symporter which creates a transmembrane gradient that drags one glucose molecule in along with it (in the same direction). Later glucose will exit to the blood where it can be transported to other tissues.

Sodium/ Potassium Pump

The Sodium/ Potassium pump is located on the basolateral side of the cell. The cells need it to maintain a low amount of sodium inside the cell. Sodium gets transported into the intestinal epithelium through SGLT1. Once inside the cell, sodium must find a different way out. The Sodium/ Potassium pumps, pump out 3 Na+ for every 2 K+ that it pumps in. This mechanism uses ATP to actively drive the Na+ ions out of the cell. At this time the pump releases an inorganic Phospate, which changes it's conformational shape and triggers an affinity for Potassium once again. Notice that glucose is still in the cell at this time. It must find a different way out because the Na+/K+ pump is solely used for sodium and potassium. Remember that Glucose still needs to make it's way to the blood stream as well. That's why the cell has GLUTs!!!

GLUT 2

The teller at the "toll booth" accepts ATP cash in exchange for three Na+ cars to pass through and 2 K+ to come into the cell.

2

K+ in!

Glucose and Sodium find their way into the cell together however they must find their own way out. Glut2 is part of the GLUT family. Glut 2 can be found in the kidney, pancreas and the intestines. In this case, Glut 2 will be transporting Glucose from the intestinal epithelium into the blood stream.

SGLT1 represented by this traffic controller, allows the passage of Na+ ions and Glucose molecules into the cell from the lumen of the intestines. Sodium is represented by the red cars, and Glucose is represented here as a silver car.

3Na+ out!

TOll Roads and tellers!

EPITHELIAL CELL

I like to think of the lumen of your Intestines as a Highway for the things you eat. Sodium, Potassium, Glucose, Fructose are just some of the things we enjoy eating everyday. Basically, they can be viewed as little cars, bikes, or trucks traveling down the highway (your intestines). They all want to get to their jobs (their destinations), so that they can get to work on keeping your body alive and well. Think of your bloodstream as another highway where cars (sodium, potassium, glucose, etc) are driving around. In order for the cars to get from one highway to the other (intestines to extracellular fluid), they will need to use smaller roads or bridges (intestinal epithelium) that connect the two. However, these roads and bridges have toll roads and traffic controllers that regulate the amount of cars that can pass through to the other highway at a given time. The Traffic controlllers (represented in my illustration as a man), are the SGLT1 symporters that allow only the glucose cars and the sodium cars to drive through into the intestinal epithelium. Each sodium has to drive to a specific "toll road", which in this case is called Na+/K+ pump in order to get out and onto the new highway (blood stream road),it must pay a "toll", or just use ATP as money. On the other hand, glucose is let's say "too big" to fit onto the same toll booth as sodium, so it has to find a booth specific for glucose molecules. Glucose specific "booths" are called GLUT2 non-toll roads, (which are represented by a purple #2 in my illustration). Also, the thick black lines in my illustration are the guard rails (cell membranes), which keep cars from driving around whereever they want to go. With the guard rails present, the cars must find toll roads and traffic controllers that will let them pass through.

Intestine lumen road

Blood stream road

Luminal membrane

(Apical side)

GLUT2 uniporter, represented by the purple #2, allows glucose to be transported across the membrane to it's destination.