Potassium homeostasis: renal contribution Flashcards
How is the large K+ difference across cell membrane maintained?
Operation of Na+K+ATPase transporter
What 3 cell functions is K+ critical for?
Regulation of cell volume
Regulation of intracellular pH
Maintaining potential difference across cell membrane
What 4 things alter plasma K+?
Food intake
Acid-Base balance
Plasma osmolality
Cell lysis and excercise
What is the initial buffer of extracellular K+ concentration?
Movement of K+ into or out of skeletal muscle
What is the internal K+ balance?
Regulation of K+ distribution between intracellular and extracellular space
What are the most important factors regulating K+ movement under normal conditions?
Catecholamines (epinephrine), insulin and aldosterone
What is the primary mechanism to prevent a rise of K+?
Uptake of K+ into the cells
What increases uptake of K+?
Epinephrine, insulin and aldosterone
How is K+ uptake achieved?
Stimulation of Na+K+ATPase, 1Na+-1K+-2CL- symporter and Na+Cl symporter
What is insulin produced by?
Beta cells of pancreas
What is epinephrine secreted by?
Adrenal medulla - activates adrenergic receptors
What is aldosterone synthesised by?
Glomerulosa cells of adrenal cortex
What determines total K+ body content?
Kidneys
Where is K+ secreted into in the nephron?
Principal cells of: Late DT
CCD
Where is K+ mainly absorbed?
PT and TAL
What is K+ reabsorption in the PCT primarily due to?
Paracellular movement via solvent drag
Shift in transepithelial voltage from -ve to +ve
What is reabsorption of K+ in TAL mainly due to?
Transcellular movement by NKCC2
Paracellular movement due to lumen positive voltage generated by K+ channels
What is DCT2 the beginning of?
Aldosterone sensitive distal nephron and electrogenic-mediated K+ transport
What channels are present in the DCT2?
ROMK channels
ENaC channels
Where is electroneutal K+Cl- cotransport present?
DCT and collecting duct
What cell surface is more permeable to K+?
Apical surface
What cell is responsible for K+ secretion in initial CD and cortical CD?
Principal cell
What pump is not present on basolateral side of type A intercalated cells?
Na+ K+ ATPase pumps
What provides the energy for the transport function of intercalated cells?
H+ gradient generated by H+ATPase pumps on apical side
When does the activity of H+K+ATPase increase?
In K+ depletion and acidosis
What 3 factors influence K+ secretion by cortical collecting ducts?
Plasma K+
Aldosterone
ADH
How does Plasma K+ determine K+ secretion during hyperkalemia?
Stimulates Na+K+ATPase -> increase K+ uptake across basolateral membrane
Increases permeability of apical membrane to K+
Increases aldosterone secretion
Increases tubular flow rate -> stimulates K+ secretion
How does Hyperkalemia stimulate aldosterone release?
Causes a direct effect on cells of zona glomerulosa of adrenal cortex
How does elevated aldosterone levels affect K+ secretion?
Increases Na+K+ATPase transporter expression in basolateral membrane
Increases ENaC expression in apical membrane -> increases electronegativity
Elevates SCK1 levels - further ENaC and K+ channel expression
Increases K+ channels on apical membrane
How does ADH affect K+ secretion?
Increases ENaC channels on apical membrane -> increases electrochemical driving force for K+ secretion
Reduces tubular flow rate -> reduces K+ secretion
Net K+ secretion not affected
How does a rise in tubular fluid flow affect K+ secretion?
Increased flow bends cillia -> cillia bend activates PKD1/PKD2 and Ca2+ entry -> imcreased Ca2+ entry actiavtes K+ channels -> K+ secretion increased
