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54. Renal Potassium Transport
Brennan
21
Biology
Graduate
10/11/2011

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Term
Effects of loss of K in cells
Definition
Cell shrinks and acidosis occurs. Loss of enzymes and slower/halted protein synthesis and stunted growth may also occur.
Term
Effects of gain of K in cells
Definition
Cells swell and alkalosis occurs.
Term
Difference in renal handling of Na and K
Definition
Na is only filtered and reabsorbed while can also be secreted.
Term
Promoters of cell uptake of K
Definition
1. Insulin
2. Aldosterone
3. Beta adrenergic agonists
4. Alkalosis
Term
Promoters of cell release of K
Definition
1. Acidosis
2. Hyperosmolarity
3. Alpha adrenergic agonists
4. Cell lysis
Term
Effect of acidosis on intracellular K content
Definition
Reduces levels of intracellular K through
1. Inhibiting Na, K ATPase
2. Inhibiting Na, K Cl Exchanger
3. Protons are bound to proteins that originally bound K. K then exits cell through K channels.
Term
How body handles excess K
Definition
Large amounts of extracellular K is fatal.
K is first stored intracellular (sequestered), before excretion 12-24 hours later.
Term
Overview of K handling in the nephron
Definition
1. 80% reabsorbed in proximal tubule
2. 10% reabsorbed in the loop of Henle
3. Distal nephron balances K levels in cell, can either reabsorb up to 8% in times of low K or secrete as much as 150% with high K levels.
Term
K handling in the proximal tubule
Definition
Paracellular
In early part of proximal tubule, there is a negative charge in lumen because of net loss of Na. Solvent drag plays a role in paracellular transport in early part of proximal tubule.
In late stage of the proximal tubule, the lumen is positive, which provides driving force for K movement into interstitial fluid.
Term
K Handling in the thick ascending limb
Definition
Transcellular
a. Lumen
Na, K, Cl Exchanger
b. Interstitial
K channel

Paracellular
Positive charged lumen creates driving force for K.
Term
Purpose of medullary K reabsorption
Definition
K reabsorption in the medulla is used to fuel the Na, K ATPase for optimal sodium reabsorption.
Term
Purpose of apical K channels
Definition
Replenishes tubular supply of K so that Na loop reabsorption is not impaired (Na, K, Cl exchanger)
Term
K handling in alpha intercalated cell of cortical collecting tubule
Definition
Lumen:
K, H antiporter
Interstitial
K channel
Term
K handling of principle cell of cortical collecting tubule
Definition
Used for secretion. During high K levels, K leaks back into lumen using K leak channels and K, Cl symporter.
Secretion is highly dependent on negative charge in lumen, which in turn is dependent on flow.
If fluid is stationary, negative luminal voltage will go away, K will dissipate charge and K secretion will stop. If flow occurs, you are taking out high K fluid and bringing in new fluid, electrical gradient maintained and negative voltage persists, allows K secretion to continue.
Term
Modulators of K secretion
Definition
Can be luminal or peritubular factors.
For luminal factors, an increased negative charge in the lumen will increase secretion. Things that dissipitate this negative charge, like secretion of K or reabsorption of Cl will inhibit further K secretion. HCO3- is impermeable, so it creates a permanent negative charge in the lumen that increases K secretion.
Term
Hyperkalemia affects on K transport
Definition
Increased cellular uptake via Na, K-ATPase
Increased aldosterone = increased secretion:
Upregulation of Na, K-ATPase activity/pump# (increases # of pumps available)
Stimulated Na reabsorption
Increased apical membrane K permeability

Hypokalemia has opposite effect.
Term
Glucocorticoid effect on K transport
Definition
Stimulate K excretion
Activate mineralocorticoid receptors
Increase GFR (increase filtered load of K)
Term
Acidemia effects on K secretion
Definition
Decreases secretion, lowered [Ki], inhibits Na, K-ATPase, lowers permeability of apical K channels
Term
Alkalemia effects on K secretion
Definition
Increases K secretion, increased [Ki], stimulates Na, K-ATPase, increases permeability of apical K channels
Term
Epinephrine effect on K secretion
Definition
Decreased K secretion
Hypokalemia
Stimulates reabsorption in IMCD
Term
Arginine Vasopressin effect on K secretion
Definition
Mixed effects, lowers urine flow (decreases negative charge in tube which decreases K secretion), but increases permeability of K and Na.
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