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Epithelial Physiology > Lecture One - Introduction > Flashcards

Lecture One - Introduction Flashcards

1
Q

Transcellular

A

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

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2
Q

Paracellular

A

transport in between cells

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3
Q

Four examples of leaky epithelia

A

proximal tubule, gallbladder, small intestine and chloroid plexus

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4
Q

Three examples of tight epithelia

A

Distal tubule, stomach and frog skin

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5
Q

what was frog skin used for?

A

model epithelium for understanding net transport pathways

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6
Q

Net transport occurs due to…

A

presence of different transport proteins on basolateral and apical membranes

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7
Q

Rte

A

Transepithelial resistance

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8
Q

Define transepithelial resistance

A

resistance across the epithelium to movement

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9
Q

High Rte

A

not a lot of transport across the epithelium in either direction

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10
Q

High Rte is usually….

A

tight epithelia

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11
Q

High Rte is typically….

A

larger than 2000 ohms cm2

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12
Q

Low Rte

A

lots of net transport

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13
Q

Low Rte is usually…

A

leaky epithelia

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14
Q

Low Rte is typically….

A

under 200 ohms cm2

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15
Q

Net transport for transcellular is…

A

similar for all epithelia

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16
Q

What decides if a cell is tight or leaky?

A

typically paracellular (transport between cells)

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17
Q

Vte in leaky epithelia

A

0mV

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18
Q

Vte in tight epithelia

A

50mV

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19
Q

Flux in leaky epithelia

A

typically large as it is isosomotic

20
Q

Flux in tight epithelia

A

small

21
Q

Leaky epithelia has … H2O permeability

A

high

22
Q

Tight epithelia has … H2O permeability

A

low

23
Q

Vte

A

transepithelial potential

24
Q

Define transepithelial potential

A

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

25
Q

Define isosmotic

A

movement by ions and solutes is followed by water

26
Q

negative Vte means

A

more anions or less cations

27
Q

positive Vte means

A

less anions or more cations

28
Q

How is Vt generated?

A

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

29
Q

Principal cell negative Vte example

A

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

30
Q

Thick ascening limb positive Vte example

A

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

31
Q

Intracellular microelectrode measures

A

intracellular potential

32
Q

Patch clamp measures

A

single or whole cell current

33
Q

Two electrode voltage clamp measures

A

cell current

34
Q

Ussing chamber measures

A

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

35
Q

describe the Ussing chamber set up

A

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

36
Q

Two electrodes in Ussing chamber function

A

measure Vte directly by comparing reference and recording

37
Q

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

A

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

38
Q

Ohms law

A

V = I*R

39
Q

Ohms law to measure Rte

A

Rte = change in V/ I injected

40
Q

Ohms law to measure Isc

A

Vte/Rte

41
Q

what is the absolute Vte

A

the Vte with no current injected

42
Q

What is Jnet?

A

Isc

43
Q

Tracer studies

A

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

44
Q

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

A

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

45
Q

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

A

CFTR and ENaC

46
Q

Describe the upper airway model

A

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

47
Q

Balance between Chloride secretion and sodium reabsorption in upper airway model

A

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

Epithelial Physiology (12 decks)

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