Lecture One - Introduction

Question 1

Transcellular

Answer 1

transcport via the cell, i.e. basolateral to apical or vice versa

Question 2

Paracellular

Answer 2

transport in between cells

Question 3

Four examples of leaky epithelia

Answer 3

proximal tubule, gallbladder, small intestine and chloroid plexus

Question 4

Three examples of tight epithelia

Answer 4

Distal tubule, stomach and frog skin

Question 5

what was frog skin used for?

Answer 5

model epithelium for understanding net transport pathways

Question 6

Net transport occurs due to…

Answer 6

presence of different transport proteins on basolateral and apical membranes

Question 7

Rte

Answer 7

Transepithelial resistance

Question 8

Define transepithelial resistance

Answer 8

resistance across the epithelium to movement

Question 9

High Rte

Answer 9

not a lot of transport across the epithelium in either direction

Question 10

High Rte is usually….

Answer 10

tight epithelia

Question 11

High Rte is typically….

Answer 11

larger than 2000 ohms cm2

Question 12

Low Rte

Answer 12

lots of net transport

Question 13

Low Rte is usually…

Answer 13

leaky epithelia

Question 14

Low Rte is typically….

Answer 14

under 200 ohms cm2

Question 15

Net transport for transcellular is…

Answer 15

similar for all epithelia

Question 16

What decides if a cell is tight or leaky?

Answer 16

typically paracellular (transport between cells)

Question 17

Vte in leaky epithelia

Answer 17

0mV

Question 18

Vte in tight epithelia

Answer 18

50mV

Question 19

Flux in leaky epithelia

Answer 19

typically large as it is isosomotic

Question 20

Flux in tight epithelia

Answer 20

small

Question 21

Leaky epithelia has … H2O permeability

Answer 21

high

Question 22

Tight epithelia has … H2O permeability

Answer 22

low

Question 23

Vte

Answer 23

transepithelial potential

Question 24

Define transepithelial potential

Answer 24

net transport of ions and charge generates a potential across the epithelium

Question 25

Define isosmotic

Answer 25

movement by ions and solutes is followed by water

Question 26

negative Vte means

Answer 26

more anions or less cations

Question 27

positive Vte means

Answer 27

less anions or more cations

Question 28

How is Vt generated?

Answer 28

sum of basolateral and apical membrane potentials, determined by net movement of charge

Question 29

Principal cell negative Vte example

Answer 29

ATPase and K+ basolateral channels set the driving force for sodium uptake, so sodium enters the cell and then pumped out the basolateral membrane. Net movement of positive charge from the apical to basolateral membranes therefore loss of positive charge results in a negative charge

Question 30

Thick ascening limb positive Vte example

Answer 30

ATPase and K+ channel drives NKCC2, which is electro-neutral. Sodium and chloride is reabsorbed but K+ is recycled through ROMK. less anions therefore positively charged

Question 31

Intracellular microelectrode measures

Answer 31

intracellular potential

Question 32

Patch clamp measures

Answer 32

single or whole cell current

Question 33

Two electrode voltage clamp measures

Answer 33

cell current

Question 34

Ussing chamber measures

Answer 34

transepithelial potential and resistance which can then be used ot measure short circuit current

Question 35

describe the Ussing chamber set up

Answer 35

two blocks of perspex with the epithelium of interest clamped in between. Epithelium is perfused with Krebs/ringer solution. use buffer to maintain pH. Reference and recording electrode, second set of electrodes connected to a current electrode box

Question 36

Two electrodes in Ussing chamber function

Answer 36

measure Vte directly by comparing reference and recording

Question 37

Second set of electrodes connected to a current electrode box in Ussing chamber function

Answer 37

allows injection of a known current across the entire cell membrane to cause a Rte shift but the amount of change is dependent on the reisstance

Question 38

Ohms law

Answer 38

V = I*R

Question 39

Ohms law to measure Rte

Answer 39

Rte = change in V/ I injected

Question 40

Ohms law to measure Isc

Answer 40

Vte/Rte

Question 41

what is the absolute Vte

Answer 41

the Vte with no current injected

Question 42

What is Jnet?

Answer 42

Isc

Question 43

Tracer studies

Answer 43

take radioactive sodium24 in apical solution and measure how much appears in basolateral membrane to measure influx and vice versa for outflux

Question 44

what proteins are present on basolateral membrane of the upper airway model?

Answer 44

Na+/K+ATPase, basolateral K+ channel and NKCC1

Question 45

What proteins are present on the apical membrane of the upper airway model?

Answer 45

CFTR and ENaC

Question 46

Describe the upper airway model

Answer 46

Sodium influx driving force on basolateral membrane set by NKCC1 Chloride accumulates in cell to above the electrochemical equilibrium so CFTR has net chloride secretion. Driving force for sodium reabsorption through ENaC

Question 47

Balance between Chloride secretion and sodium reabsorption in upper airway model

Answer 47

sets the height of the pericilliary layer which is the first line of defence against infection