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PHSL233 Cellular, GI and Renal > Lab 3 - Epithelia > Flashcards

Lab 3 - Epithelia Flashcards

1
Q

What is equilibrium?

A

A state of balance due to the equal action of opposing forces.

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2
Q

Are there ions moving with a solution is at equilibrium?

A

Yes there are unidirectional ion fluxes - but there is no visible net changes in ion concentration because there is an equal number of ions flowing in each direction

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3
Q

What is a membrane potential?

A

A difference in the electrical potential between the inside and the outside of a cell membrane.

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4
Q

What equation is used to work out the theoretical membrane potential?

A

Nernst Equation (Ex)

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5
Q

What unit is T in?

A

Kelvin

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6
Q

Is the luminal concentration ECF or ICF?

A

Extracellular

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7
Q

What are the units for amplitude?

A

mV

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8
Q

What are the units for duration?

A

ms

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9
Q

What are the units for frequency?

A

Hz

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10
Q

What is Ohms law?

A

I = V/R

Current = voltage / resistance

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11
Q

What is the relationship between concentration and voltage?

A

Proportional

The larger the concentration gradient, the larger the membrane potential.

The larger the chemical driving force, the larger the electrical driving force required to balance it and maintain equilibrium.

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12
Q

What is the units for membrane potential?

A

mV

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13
Q

What is the units for concentration?

A

mmol L-1

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14
Q

When graphing voltage / concentration what is on the x axis?

A

Concentration

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15
Q

What is the key properties that may change the membrane potential between the measured and calculated values?

A

temperature

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16
Q

What are the four reasons why measured and calculated membrane potential may be different?

A

Temperature

The calculated values presume the membrane is only permeable to small cation (but it may be slightly permeable to anions also).

They presume that K+ is the only cation present (but there may be H+ if further dissociation)

They presume the concentrations of the solution is exactly as stated (but there may be small differences in the actual concentration of solutions compared to the theoretical concentrations of solutions - e.g., if some water evaporated or if the chambers were not properly washed).

17
Q

What is the driving force in step 1 of forming the transmembrane voltage?

A

Chemical driving force

18
Q

What is the driving force in step 2 of forming the transmembrane voltage?

A

Electrical driving force

19
Q

What meant that the artificial cell membrane could come to equilibrium?

A

Because we don’t have a Na/K-ATPase maintaining the RMP

20
Q

What is the Goldman-Hodgkin-Katz equation?

A

Vm = RT/F x In (permeability x concentration outside for K + Na and permeability x concentration inside for Cl-) / (opposite)

21
Q

What is the key thing you need to remember to do once initially working out Vm?

A

convert from V to mV (x1000)

22
Q

When should there be no voltage generation?

A

When there is no net difference in the molar concentration of cations across the artificial membrane

23
Q

What are the two reasons why the calculated membrane potential between nerve cell and artificial membrane is different?

A

Different permeabilities to cations
Different permeabilities to anions

24
Q

Why does a nerve cell and artificial membrane have different permeabilities to cations?

A

Because nerve cell has ion channels and transporters that are selective for specific cations: different channels = different permeability for K+ compared to Na+.

Whereas the artificial membrane just has cation selective pores and is equally permeable to all actions = the same permeability for K+ and NA+

25
Q

Why does a nerve cell and artificial membrane have different permeabilities to anions?

A

A nerve cell has some permeability to Cl- whereas the artificial membrane is not permeable to Cl- (the movement of Cl- influences the membrane potential).

26
Q

What is overall transport across membrane dependant on?

A

Tissue surface area

27
Q

Which transport protein is responsible for establishing the active driving force for ion transport in living cells?

A

Na+/K+ ATPase (example of primary active transport - uses ATP to transport against an electrochemical gradient)

28
Q

To measure active transport in a living epithelium what would the transepithelial voltage have to be initially?

A

The transepithelial voltage to be 0 - therefore the active transport would then generate the voltage we would short circuit

29
Q

What generates the short circuit current?

A

The voltage clamp

30
Q

Why is it called a short circuit current?

A

Because it is the amount of current required to short the voltage back to 0

31
Q

What is the equation for epithelia resistance?

A

R = change in V / change in current

32
Q

Does leaky or tight epithelia have a lower resistance?

A

Leaky

33
Q

If you increase voltage what happens to resistance?

A

Nothing - because an increased voltage also increases the current

PHSL233 Cellular, GI and Renal (13 decks)

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