Aquaporin-1 Essay -- Biology Aquaporin

Background Most modern biology textbooks will tell you that low-molecular-weight molecules like CO2, NH3 (ammonia), and urea cross cell membranes by simple diffusion. Some scientists postulate, however, that specific pores mediate this transport. A recent study conducted to further this hypothesis examines expression of the water channel aquaporin-1 (AQP-1) and its enhancing affect on CO2 permeation into cells. Why would scientists challenge the traditional simple diffusion theory? Two strong points of evidence led to this experiment: First, many cell membranes have a very low permeability to small molecules: The outer membranes of some gastric glands allow very little CO2 to enter the cell, while most frog egg cells have membranes that act as virtual barriers to the harsh materials present in their environment. If the simple diffusion theory is correct, diffusion of small molecules into cells should be an unregulated process. If diffusion is an unregulated process, how could some cells have a lower permeability to small molecules than others? Second, scientists have already found membrane proteins that facilitate the entrance of water and urea: While the UT2 protein enables transport of urea past the cell membrane, an entire class of membrane proteins called the aquaporins enable the permeation of water into cells. If small molecules enter the cell by diffusion, why would the cell have extra mechanisms to facilitate their entry? Any Questions? Q) What's this diffusion thing you keep talking about? A) Particles randomly flow from areas of high concentration (a lot of particles) to areas of low concentration (not many particles) until they are evenly dispersed. If you've ever put a normal cell in a c... ...ially exciting opportunity to manipulate gas transport rates lies in cancer research, where inhibiting the transcription of AQP-1 could be the key to killing cancer cells . Cancer cells release more CO2 than most other cells, so stopping these cell's abilty to extrude the gas to their environment would result in cell death. This example is one of many uses for the manipulation of gas transport, however, and the opportunities are endless. The idea that gas transport is actively mediated by the cell is a huge paradigm shift from the traditional belief that transportation is uncontrolled. Further studies (Cooper and Boron, Am. J. Physiol. In press) have proven the conclusion drawn from this experiment, and the search for pores that mediate transport of specific gasses has already begun. The diffusion dogma has been destroyed, and the textbooks will be re-written.