Session 6 - Control of Potassium (OK+?) Flashcards
What % of K+ is in the ICF?
- 98%
* 120-150mmol
What % K+ is in the ECF?
- 2%
* 3.5 - 5 mmol/l
What is the difference between ICF & ECF maintained by?
Na+/K+ ATPase
How does K+ establish the resting membrane potential?
- Diffusion out of ICF into ECF
* Gives resting cell membrane potential of -90mv
What does an increase in ECF K+ cause?
• Depolarisation of cell membrane
What do a decrease in ECF K+ cause?
Hyperpolarization of the cell
Give a brief overview of K+ ions
- K+ ions are the most abundant intra-cellular cation
- 98% of total body K+ content is intracellular
- 2% is in the ECF
Body tightly maintains plasma K+ in the range of 3.5 - 5.3 mmo
Why is high K+ inside cells and mitochondria necessary?
Maintaining cell volume Regulating intracellular pH Controlling cell-enzyme function DNA/Protein synthesis Cell growth
What are the metabolic effects of extremely low extracellular K+?
- Inability of the kidney to form concentrated urine
- A tendency to develop metabolic alkalosis
Large enhancement of renal ammonium excretion
Why is low K+ necessary outside cells?
- To maintain steep K+ ion gradient across cell membranes
- Increase in ECF K+ depolarises cell membrane
- Decrease in ECF K+ hyperpolarises the cell membrane
How is potassium regulated?
- Internal balance, maintaining ECF K+
* External balance, adjusts K+ excretion to intake
What is average K+ intake in diet?
40 - 100 mmol/day
How does body prevent huge increase in ECF K+ after eating?
- K+ moves into cells
* Kidneys begin to excrete K+
What is internal balance the net result of?
- Movement of K+ from ECF -> into cells
* Movement of K+ out of cells into ECF
What factors promote the uptake of K+ into cells?
• Hormones ○ Insulin ○ Aldosterone ○ Catecholamines • Alkalosis ○ Shift of H+ out of cells ○ Reciprocal K+ shift into cells • Increased K+ in ECF
How does insulin promote uptake of K+ in ECF?
• K+ in splanchnic blood stimulates insulin secretion by pancreas
Insulin stimulates K+ uptake by muscle cell and liver via an increase in Na+/K+ ATP-ase
How does aldosterone promote excretion of K+ into tubule lumen
- Increases the transcription of Na/K/ATPase in basolateral membrane and ENaC/K+ channels in apical membrane
- Increased channel number gives increases K+ excretion
What factor can stimulate aldosterone secretion?
• Hyperkalaemia
How do catecholamines increase uptake of K+ in ECF?
• Act via B2 adrenoreceptors which in turn stimulate Na-K+-ATPase
Outline 5 factors promoting K+ shift out of cell
• Low ECF • Exercise • Cell lysis • Increase in ECF osmolality • Acidosis - Increase ECF ○ Acidosis, shift of H+ into cells, reciprocal K+ shift out of cells
How does exercise promote K+ shift of cells?
- Skeletal muscle contraction -> Net release of K+ during recovery phase of action potential
- Increase in plasma K+ which is proportional to the intensity of exercise
- Uptake of K+ by non contracting tissues as a result of catecholamine release
How do catecholamines offset ECF rise in K+ during exercise?
• By increasing K+ uptake to other cells
How does cell lysis promote K+ shift out of cells
- Cell lysis causes a release of K+ from ICF into the ECF
* Can be causes by skeletal muscle trauma, intravascular haemolysis and cancer chemotherapy
How does plasma tonicity cause K+ movement from ICF to ECF?
- Increase in plasma & ECF tonicity
- Water moves from ICF into ECF
- Increase in K+ in ICF
K+ moves down conc grad out of cell
What does acidosis do to K+ conc in cell?
- Shift of H+ into cells
- Reciprocal K+ shift
- Out of the cells
- Causes hyperkalaemia
What does akalosis do to K+ concentration in cell?
- Shift of H+ out of cells
- Reciprocal K+ shift
- Move into cells causes hypokalaemia
