Lecture 1 Flashcards
What are the 2 different types of transport?
Transcellular - move across apical and basolateral membrane
Paracellular - movement between the cells
Examples of leaky epithelia?
o proximal tubule
o gallbladder
o small intestine
o choroid plexus
Examples of tight epithelia?
o distal tubule
o stomach
o frog skin
Difference between tight and leaky transepithelial resistance?
o Leaky < 200 .cm2 ow resistance – lots of net movement – high absorption
o Tight > 2000 .cm2 High resistance – not a lot of movement across epithelia – more transcellular movement, not a lot of movement between cells.
what is transepithelial resistance determined by?
paracellular permeability
its resistance across epithelia to movement
What are the properties of leaky epithelia
o Rte < 200 .cm2
o Vte ~ 0mV – can’t sustain potential due to gaps between cells being so leaky
o Flux large isosmotic = followed by water
o High H2O permeability
o Transcellular and paracellular
What are the properties of tight epithelia?
o Rte > 2000 .cm2
o Vte ~ 50mV
o Flux small – only transcellular
o Low H2O permeability
What is transepithelial membrane potential the sum of?
apical and basolateral membrane potentials
What is the transepithelial membrane potential of principal cell in the collecting duct?
o ENac on apical surface
o Na/K ATPase and a K channel on basolateral surface
o Electrochemical driving force for Na uptake from apical membrane out of basolateral membrane
o Negative Vt
What is the transepithelial membrane potential of thick ascending limb?
o Na/K ATPase and a K channel and Cl channel on basolateral surface
o K channel and NKCC2 on apical channel
o 2 positive charges and 2 neg charges on NKCC2 = electroneutral transport protein – no net movement of charge
o Na, Cl reabsorbed
o K recycled
o Only 1 net positive charge
What does a Intracellular microelectrode measure?
IC potential (Vm)
what does a patch clamp measure?
Single channel/ cell current – only uses 1 electrode – for smaller cells
what does a 2 electrode voltage clamp measure?
Cell current – use on larger cells
what does a ussing chamber measure?
Transepithelial potential, transepithelial resistance, Short circuit current.
o Look at whole epithelial function - how a whole epithelium behaves
o Use potential and resistance values to calculate short circuit current
o Cannot calculate net current directly need to derive it using equivalent short circuit current
what is the set up for an ussing chamber?
• 2 blocks of Perspex
• Clamp tissue you want to look at and place between the 2 blocks of Perspex.
• Epithelia is perfused with Krebs or ringer solution (bicarbonate buffer – make sure pH is at 7.4)
• 4 electrodes – 1 is reference 1 is set to record – measure transepithelial potential
• First set of electrodes Measure transepithelial potential
• Second set of electrodes
o Connected to current injection box – inject current across epithelia
o Known current is injected
o Transepithelial potential shifts
o How much it shifts depends on resistance of the epithelium
o Measure change
o Can work out transepithelial resistance using Ohms law
