Epithelial Transport Flashcards
What are the basic characteristics of an epithelial cell?
- line hollow organs or tubes - regulate the abosrption/ secretion across the surface
- have tight junctions that restrict the passive diffusion of ions across the epithelial layer
- one faces the hollow/fluid filled chamber (luminal, apical, mucosal)
- the opposite surface is normal close to a network of blood vessels (basolateral, serosal membrane)
Give 5 areas that have epithelial lining and their purpose
- Lung - lung growth, management of pericillary fluid layer
- Kidney - maintenance of salt and water balance
- Gut - absorption of nutrients, salt and water
- Exocrine glands - secretion of fluid
- choroid plexus - regulation of CSF composition
Why is the pulmonary epithelium important?
- Aid the production of surfactant
- move ions so there is enough fluid for surfactant to work
What are tight junctions?
- matrix of wiggly lines - looks like a net
- fit between two surfaces of the cells and act like a sieve - restrict movements of ions and solutes
- can select whether cations or anions pass through
Primary active transport
The movement of molecules against their concentration gradient from a low concentration to a high concentration
- requires ATP
Passive transport
Movement of molecular substances across cell membranes without need of energy input.
- from high concentration to low concentration
What are the transporting cells of the pulmonary epithelium?
- Type 1 - squamous cells. Involved in the process of gas exchange - very thin to accommodate this. Cannot
- Type 2 - secrete pulmonary surfactant - decreases surface tension in alveoli
- clara cells - have small microvilli. secrete glycosaminoglycans to protect the bronchioles
Apical vs basolateral uptake
- put different known drugs on each side - such as Na/K channel blocker - see if it has an effect on either side - if yes, then there is the exchanger on that
Measuring transepithelial transport
- Mice with CF mutation
- Normally have Na absorption and Cl secretion.
- Adding forskolin increases cAMP levels, which activates Cl- secretion
- Na movement drives fluid absorption, Cl movement drives fluid secretion
- The 2 balance fluid between them by osmosis
- hang up bit of tissue and measure amount of fluid leaving tube into bath
- before addding forskolin, normal and CF mice will be absorbing fluid via Na movement
- after adding forskolin, normal mice will start secreting fluid, whereas CF mice will continue to absorb as they dont have CFTR
How would you look at water passing through an epithelium (whole organ)
- Radioisotope tracers
- non-absorbable markers- see if the markers are being diluted etc
- Gravimetric methods - epithelial tube in a bath, can record the weight and see what happens to fluid movement in or out when you add drugs. can invert it so membrane is other way around
Looking at fluid uptake in lung
infuse fluid into lungs with dye, leave over period of time and then keep sampling
- can see if the dye is getting more concentrated = fluid absorbed-
Ussing Technique - isolated epithelium
- put epithelial cells in a chamber - bathe either side
- have electrodes either side measuring voltage and current
- can measure voltage across membrane by the movement of ions
- if sodium is moving across, you will get a build up of positive charge on one side compared it the other
- transepithelial potential
- can use ohms law (V=IR)
- if you know the resistance and voltage you can calculate I
- if you make the difference between the two sides 0, you pass a current in the equal and opposite direction. the current flow required is short circuit current
Measuring ion flux using radiotraces
- put radiotracer in apical bath, see how much ends up in basolateral bath and vice versa
- ussing flux says that if a movement from A to B is the same as B to A - its probably just diffusion
- If one exceeds the other, there is active transport
