Question

The gram-negative bacterium Vibrio cholerae produces a protein, cholera toxin (Mr 90,000), that is responsible for the characteristic symptoms of cholera: extensive loss of body water and NaCl through continuous, debilitating diarrhea. If body fluids and NaCl are not replaced, severe dehydration results; untreated, the disease is often fatal. When the cholera toxin gains access to the human intestinal tract it binds tightly to specific sites in the plasma membrane of the epithelial cells lining the small intestine, causing adenylyl cyclase to undergo prolonged activation (hours or days).
a. What is the effect of cholera toxin on [cAMP] in the intestinal cells? Why?
b. Based on the information above, suggest how cAMP normally functions in intestinal epithelial cells. Briefly justify.
c. Suggest a possible treatment for cholera

Answer 1

Answer:

a.) It causes prolonged activation of adenylyl cyclase which leads to increased levels of Cyclic adenosine monophosphate(cAMP).

b.) In the intestinal epithelial cells, the cAMP binds to the apical chloride channels and allows it to open leading to osmotic permeability of water across the cell into the lumen of the intestine which is excreted through the faeces.

C.) Cholera can effectively be treated through the use of antibiotics and intravenous fluid replacement therapy.

Explanation:

Vibrio cholerae is a gram negative rigid curved bacillus that are actively ( vigorously) motion by a polar flagellation. The name vibrio is derived from the characteristic vibration movement of the organism when viewed under a microscope. This bacteria is capable of producing toxins called cholera toxin, which it uses as a virulent factor. It is responsible for the characteristic symptoms of cholera: extensive loss of body water and NaCl through continuous, debilitating diarrhea.

Cyclic adenosine monophosphate(cAMP) which is called a second messenger because it is not a hormone that can directly institute an intracellular change, instead, it serves as a second messenger to cause an effect.In the intestinal epithelial cells, the cAMP binds to the apical chloride channels and allows it to open leading to osmotic permeability of water across the cell into the lumen of the intestine which is excreted through the faeces.

In the effect of cholera toxin on the cAMP in the intestinal cells, Cholera toxin increases the fluid loss. The binding of the toxin to the intestinal cells causes a large increase in the level of cAMP in the cells by inhibiting the conversion of GTP bound to Ga to GDP. So adenyl cyclase is not turned off and diarrhea results.

The possible treatment is through the use of antibiotics and intravenous fluid replacement therapy. Prompt and adequate replacement of lost fluid and electrolyte through oral administration and supplemented with intravenous administration of fluids highly suggested for treatment of cholera. Antibiotics is equally used for treatment only when the cholera strain has been confirmed sensitive to it through culture.