User:Ecessford

Erin Cessford

UWO Biology 4931G - Seminar in Physiology

Article Choices for Wikipedia Update Assignment

Wikipedia does not have a page on teleost chloride cells. Chloride cells are located within teleost gills and are used for osmoregulation. I would like to add a page on this topic to discuss the basal membrane KNCC transporter and the apical cystic fibrosis transmembrane conductance receptor (CFTR) used to facilitate transcellular ion transport from the blood, through the cell and into the external water.

The second article option I would like to add information to is on the insect malpighian tubule system. This article is lacking important information regarding structure and osmoregulation function. I would like to address the cells comprising the tubule, which include principle and stellate cells, as well as the functions of these cells.

The third potential article topic I would like to build upon is resilin. There is very little information regarding this elastic storage molecule. Resilin stores a huge amount of elastic energy and is responsible for transmitting the great force used by fleas to jump.

The last possible topic I would like to contribute more information to is on the woolly bear caterpillar. Wikipedia touches on the overwintering strategies of these caterpillars, however, I feel that more physiological information regarding the mechanisms that allow for freeze-tolerance should be discussed. I believe that this article should explain the caterpillars reduction in supercooling point as a result of glycerol production, an important cryoprotectant.

Teleost chloride cells is a good choice.

Osmoregulation Article Edits

Article to review: Osmoregulation

The Wikipedia article detailing osmoregulation makes a very brief reference to teleost chloride cells, also referred to as mitochondria-rich cells, but is lacking an explanation on the important physiological function of these cells. Teleost gills are multifunctional organs that have significant roles in ion transport, nitrogenous waste excretion, gas exchange and regulation of acid-base balance. In terms of ion transport, chloride cells are vital for ensuring body fluid homeostasis, especially within a salty marine environment. Chloride cells are structurally similar in freshwater and saltwater teleosts but are functionally very different. I believe that a physiological explanation on chloride cell function in saltwater and freshwater fish would improve Wikipedia’s description of osmoregulation. For the purpose of this assignment, I would like to only address the primary mechanisms involved in the process of active salt extrusion within hyposmotic marine teleosts, as it would greatly enhance the understanding of how osmoregulation occurs at the gills in a desiccating saline environment.

The Wikipedia osmoregulation page states that hyposmotic marine fish have a tendency to lose water and gain salt across the gills, however the role of salt secretion via chloride cells is barely touched on. Chloride cells are specialized ionocytes that make up about 10% of the brachial epithelium. Several key ion transporters that move ions into and out of the fish are found along the basolateral and apical membrane of chloride cells. In particular, a Na+/K+-ATPase located along the basal membrane moves 3Na+ out of the animal and 2K+ into the animal thereby establishing a strong negative cytosolic membrane potential that generates the driving force required for the ionic uptake of sodium, potassium and chloride via a basal Na+/K+/2Cl− co-transporter. Chloride cells are rich in mitochondria to ensure that high levels of ATP are available to fuel Na+/K+-ATPases. Chloride ions are actively transported into the seawater while sodium ions are passively transported. Potassium leak channels are also found along the basal membrane ensuring that some potassium is transported back into the blood as a way to maintain membrane potential.

Apical cystic fibrosis transmembrane conductance regulator (CFTR) ion transporters enable the transcellular diffusion of chloride ions into the seawater. In contrast to chloride ion extrusion, sodium ions are transported out of the teleost gills via paracellular channels and leaky junctions located in between a chloride cell and an adjacent accessory cell. Chloride cells are found in a multicellular complex with accessory cells, and together, this complex functions as the active unit for NaCl extrusion. Another interesting aspect of chloride cells is the fact that they exhibit plasticity. Specifically, the apical crypt of chloride cells can change with varying salinities ranging from a deep hole in high salinities, a shallow hole in intermediate salinities or villi covered in ion-poor freshwater as an attempt to increase the surface area available for transport. Chloride cell plasticity is indicative of the importance of osmoregulation at the gills.

The three key references I would cite to support my explanation include the following:

Evans et al. (2005) explains the gill functions with respect to ion transport, nitrogenous waste excretion, gas exchange and acid-base balance regulation. The main points I would use from this article to improve the Wikipedia page on osmoregulation would include:

• Fish gills are multipurpose organs
• Chloride cells occupy approximately 10% of the brachial epithelium
• Chloride cells play an important role in NaCl secretion in seawater teleosts
• Lastly, marine teleosts express in a chloride cells in a multicellular complex involving smaller accessory cells

Hwang and Lee (2007) outline the regulatory molecular mechanisms of ion transport in teleost gills. I would address the following points from this article in my Wikipedia update:

• Fish in elevated saline environments are faced with difficult osmotic and ionic gradients
• Marine teleosts actively secrete ions through the gills to maintain body fluid homeostasis
• Direction of ion transport reversed in freshwater and saltwater teleost gills
• Chloride cells are specialized ionocytes that are the primary cell type for active salt extrusion from the gills

Finally the paper by Marshall and Grosell (2005) goes into great detail on the various osmoregulatory strategies found in freshwater and marine teleosts. I would like to use these specific points in my Wikipedia update to better explain chloride cell anatomy and function:

• Leaky junctions are found between chloride cells and accessory cells
• Some potassium is transported back into the marine teleost blood to maintain membrane potential
• The apical surface of chloride cells are quite plastic. Specifically, the apical crypt of chloride cells can change with varying salinities ranging from a deep hole in high salinities, a shallow hole in intermediate salinities or villi covered in ion-poor freshwater to increase the surface area for transport
• A detailed figure similar to Figure 6.4 in this paper should be used in conjunction with the text explaining the osmoregulatory function of chloride cells to help the reader better understand this process

Citations:

Evans, D. H., Piermarini, P. M. and Choe, K. P. (2005). The multifunctional fish gill: dominant site of gas exchange, osmoregulation, acid-base regulation, and excretion of nitrogenous waste. Physiological Reviews 85: 97−177

Hwang, P.P. and Lee, T.H. (2007) New insights into fish ion regulation and mitochondrion-rich cells. Comparative Biochemistry and Physiology A 148: 479−497

Marshall, W.S. and Grosell, M. (2005) Ion transport, osmoregulation and acid–base balance. In: D. Evans and J.B. Claiborne (eds) Physiology of Fishes, 3rd edn, pp. 177–230. CRC press, Boca Raton