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ESA1 - Physiology and Pharmacology > ATP Dependent Pumps and Ion Exchangers > Flashcards

ATP Dependent Pumps and Ion Exchangers Flashcards

1
Q

What are the functions of the Na pump?

A

1) Forms Na+ and K+ gradients but only contributes abut -5mV to the resting membrane potential. Main contributor is efflux of potassium ions
2) Drives secondary active transport

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2
Q

What are some examples of the Na pump driving secondary transport?

A

Control of intracellular pH
Regulation of cell volume
Regulation of intracellular calcium concentration
Absorption of Na+ in epithelia
Nutrient uptake eg glucose in the small intenstine

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3
Q

What is intracellular [Ca2+] and what is extracellular [Ca2+]?

A

Intracellular = 100nM (or 0.1 micromoles or 0.0001 millimoles)

Extracellular = 1-2mM

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4
Q

In which tissues would extracellular calcium levels be at the higher end of 1-2mM?

A

Eg bone

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5
Q

In which tissues would extracellular calcium levels be at the lower end of 1-2mM?

A

Eg muscle

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6
Q

What is the difference in calcium levels across the plasma membrane?

A

10,000 to 20,000 fold

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7
Q

As cells are signalled by small changes in intracellular [Ca2+], roughly how much is needed to signal?

A

About 20nM

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8
Q

Is PMCA a primary or secondary transporter?

A

Primary active transporter

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9
Q

Why isn’t SERCA a pump?

A

It is not on the plasma membrane

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10
Q

Where is an example of Ca2+ uniporters?

A

Ca2+ being transported into the mitochondria (Mitochondrial calcium uniporter)

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11
Q

When do mitochondrial calcium uniporters operate?

A

At high intracellular calcium levels to buffer potentially damaging [Ca2+]

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12
Q

What are the two primary active transporters involved in control of resting [Ca2+]i?

A

PMCA (expels Ca2+ out of the cell)

SERCA (accumulates Ca2+ into SR/ER)

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13
Q

What is the affinity compared to the capacity of both PMCA and SERCA?

A

High affinity, low capacity

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14
Q

What is the secondary active transporter involved in control of resting [Ca2+]i?

A

NCX

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15
Q

What is the affinity compared to the capacity of NCX?

A

Low affinity, high capapcity

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16
Q

What is the role of NCX?

A

Expels intracellular Ca2+ during cell recovery by exchanging 3 Na+ for 1 Ca2+

17
Q

What is meant by the electrogenic nature of NCX?

A

Current flows in the direction of the Na+ gradient.

18
Q

If the cell is depolarised, which way does NCX function?

A

Moves 1 Ca2+ in for 3Na+ out

19
Q

What happens to the NCX in ischaemia?

A

ATP is depleted so the sodium pump is inhibited, leading to the accumulation of sodium ions inside the cell and causing the cell to be depolarised. The NCX therefore reverses and moves one calcium ion in for every three sodium ions out. High intracellular calcium levels are toxic.

20
Q

What exchangers are involved in control of cell pH?

A

Na+/H+ exchanger (NHE)
Cl-/HCO3- exchanger
NBC (sodium bicarbonate cotransporter)
Anion exchanger

21
Q

What does the Na+/H+ exchanger do?

A

Exchanges extracellular Na+ for intracellular H+
Electroneutral 1:1 exchange
Regulates pH intracellularly and cell volume

22
Q

What is NHE inhibited by?

A

Amiloride (a potassium sparing diuretic - stops potassium entering urine)

23
Q

What transporter alkalinises the cell?

A

Na+-bicarbonate-chloride cotransporter (NBC)

24
Q

What transporter acidifies the cell?

A

Anion exchanger (AE1) Band 3 - moves HCO3- out and Cl- in. Also holds shape of erythrocytes.

25
Q

How does the cell respond to shrinking?

A

Influx of ions so that water will enter the cell

26
Q

How does the cell respond to swelling?

A

Extrusion of ions so that water leaves the cell

27
Q

How does the kidney reabsorb all of the sodium bicarbonate filtered into the proximal tubule?

A

NHE pumps sodium ions out of the lumen of the proximal tube and into the epithelial cell and pumps H+ ions into the lumen. The sodium then enters the capillary via the Na pump. H+ ions pumped into the lumen of the proximal tube combine with bicarbonate ions to make carbonic acid which is acted upon by carbonic anhydrase to form water and carbon dioxide. Water and carbon dioxide can freely pass through the membrane into the cell. Another carbonic anhydrase then converts the water and carbon dioxide back into carbonic acid in the cell which dissociates into H+ and bicarbonate ions. The bicarbonate ions are then transported into the capillary via an anion exchanger. The H+ ions can then be reused in NHE, which drives the process.

28
Q

Why do you need bicarbonate ions?

A

Buffering capacity in blood

29
Q

How do loop diuretics work in treating mild hypertension?

A

Act on the Na+-K+-2Cl- symporter in the thick ascending limb to inhibit reabsorption of sodium, chloride and potassium ions which will stay in the lumen of the tube. Therefore the ions do not leave and water does not follow so blood pressure is controlled

30
Q

What is an example of a loop diuretic?

A

Furosemide

31
Q

What do thiazides do?

A

Inhibit reabsorption of sodium (Na+) and chloride (Cl−) ions from the distal convoluted tubules in the kidneys by blocking the thiazide-sensitive Na+-Cl− symporter

32
Q

When are thiazides often used?

A

People with type 2 diabetes

33
Q

What does Amiloride inhibit?

A

Epithelial sodium co-transporter (ENaC) thereby inhibiting sodium reabsorption in the late distal convoluted tubules, connecting tubules, and collecting ducts in the nephron.

34
Q

What does antidiuretic hormone stimulate?

A

Production of aquaporins

35
Q

What does alcohol do to antidiuretic hormones?

A

Stops the production of antidiuretic hormone so aquaporins are not produced and water is not being reabsorbed into the body so a lot of urine is produced

36
Q

What is Spironolactone?

A

Mineralocorticoid receptor antagonist - used in people with high levels of hypertension

ESA1 - Physiology and Pharmacology (11 decks)

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