Renal Regulation of ECF Potassium

Question 1

K+ concentration in the ECF determines the _____ of all excitable cells.

Answer 1

resting membrane potential.

This has a strong influence on the generation and properties of the action potentials in the nervous system and in muscle cells. For the heart, abnormalities in potassium concentrations can be especially serious in causing cardiac arrhythmias.

Question 2

True or False: the status of potassium regulation has a major effect on acid/base balance

Answer 2

True

Question 3

_____ is the most abundant ion within cells.

Answer 3

Potassium

This it contributes to the osmotic properties of the cellular compartment

Question 4

What is the range for normal ECF potassium concentration?

Answer 4

3.5 - 5.0 mM

Question 5

Insulin levels _____ after you intake potassium

Answer 5

increase

Question 6

True or False: Insulin is a major player in internal potassium balance

Answer 6

True

Question 7

True or False: potassium is freely filtered at the glomerulus

Answer 7

True. 100% of it is filtered

Question 8

Describe K+ as it goes through the nephron

Answer 8

Proximal convoluted tubule - 50% reabsorbed

Descending limb of loop of henle - 50% secreted

At hairpin turn, there is 100% of filtered potassium present

Ascending limb of loop of henle - almost all reabsorbed (90%)

Cortical collecting tubule - potassium added

Collecting duct - potassium reabsorbed

Question 9

What happens to potassium at the proximal convoluted tubule?

Answer 9

Potassium is reabsorbed passively paracellularly. It is driven by the bulk flow of water through the tight junctions.

Question 10

What happens to potassium at the ascending limb of the loop of henle?

Answer 10

Na/K/2Cl co-transporter on the apical membrane pumps in Na, K, and 2Cls. Once transported into the tubule cells, sodium ions are actively transported across the basolateral membrane by Na+/K+-ATPases, and chloride ions pass by facilitated diffusion through basolateral chloride channels. Potassium, however, is able to diffuse back into the tubule lumen through apical potassium channels, returning a net positive charge to the lumen and establishing a positive voltage between the lumen and interstitial space. This charge gradient is obligatory for the paracellular reabsorption of both calcium and magnesium ions.

Question 11

What happens at the cortical collecting tubule with potassium?

Answer 11

Na is reabsorbed through the apical membrane (ENaC). Once absorbed, it leaves the basolateral side through a Na/K-ATPase. K is now in the cell and leaves through the apical membrane.

Aldosterone receptors up and down regulate this mechanism.

This happens in principal cells

Question 12

Describe what happens to K+ in the collecting duct (medullary and papillary collecting tubule)

Answer 12

K/Cl co-transporter brings them in through the apical membrane.

There is a K+/H+-ATPase (K+ in and H+ out).

This happens in intercalated cells

Question 13

At the cortical collecting tubule, K+ secretion depends on what 2 things?

Answer 13

1. Aldosterone
2. Amount of Na in lumen. If there is no Na in lumen, it doesn’t matter how much aldosterone there is, K isn’t going to be secreted.