Regulation of Potassium

Question 1

Which is the main ion intracellularly?

Answer 1

• Potassium (K⁺)

Question 2

How is a high intracellular potassium ion maintained?

Answer 2

• By the sodium potassium ATPase

Question 3

What effect does high K⁺ have?

Answer 3

• Depolarises membranes:
  
  • ​Action potentials
  • Heart arrhythmias (Tented T waves)

Question 4

What effect does a low K⁺ have?

Answer 4

• Heart arrhythmias (asystole)

Question 5

What % of filtrate potassium is reabsorbed in the proximal convoluted tubule?

Answer 5

• 67%

Question 6

Which factors influence (increase) plasma K⁺ secretion (4)?

Answer 6

• Increased plasma potassium [K⁺]
• Increased aldosterone
• Increased tubular flow rate
• Increased plasma pH

Question 7

How does plasma [K⁺] affect K⁺ excretion (4 steps)?

Answer 7

1. Increased [K⁺]
2. Increased activity of Na⁺/K⁺ATPase
3. Decreased K⁺ return in the plasma
4. Increased K⁺ excretion

Question 8

Which cells are responsible for plasma potassium?

Answer 8

• Principal cells

Question 9

How does aldosterone affect K⁺ excretion (3 steps)?

Answer 9

1. Increased aldosterone
2. Increased Na⁺ reabsorption at DCT
3. Increased K⁺ secretion due to charge imbalance

Question 10

What type of flow regulates potassium excretion?

Answer 10

• Tubular flow

Question 11

How does plasma tubular flow affect K⁺ excretion (8 steps)?

Answer 11

1. Increased tubular flow
2. PDK1 activation
3. Increased Ca²⁺ in the cell
4. Stimulates the opening of K⁺ channels on the apical membrane
5. Increased serum [K⁺]
6. Increased activity of Na⁺/K⁺ATPase
7. Decreased K⁺ return in the plasma
8. Increased K⁺ excretion

Question 12

What effect does insulin have on potassium?

Answer 12

• Plasma insulin mediates the tissue uptake of potassium

Question 13

How does insulin mediate increased potassium uptake?

Answer 13

• Stimulates the activity of the sodium proton exchanger which increases intracellular sodium
• The increase in intracellular sodium activates sodium potassium ATPase, increasing potassium uptake

Question 14

What are the causes of hypokalaemia (5)?

Answer 14

• Common electrolyte imbalances (20% of hospitalised patients)
  
  • Inadequate dietary intake (Processed food)
  • Diuretics (Due to increase tubular flow rates)
  • Surreptitious vomiting
  • Diarrhoea
  • Genetics (Gitelman’s syndrome)

Question 15

What is Gitelman’s syndrome?

Answer 15

• Mutation in the Na⁺/Cl^- transporter in the distal nephron
  
  • Increases aldosterone synthesis in response to hyponatraemia - thus hypokalaemia

Question 16

What are the common causes of hyperkalaemia (5)?

Answer 16

• Common electrolyte imbalance present in 1-10% of hospitalised patients
  
  • Response to K⁺ sparing diuretics (spironolactone)
  • ACE-inhibitors
  • Elderly
  • Severe diabetes
  • Kidney disease