Renal K Handling

Question 1

what is the mechanism of transport for K in the proximal tubule?

Answer 1

paracellular

Question 2

how much reabsorption happens in the proximal tubule?

Answer 2

~65%

Question 3

how much reabsorption happens by the end of the loop of Henle?

Answer 3

90%

Question 4

what is the driving force for reabsorption in the TAL?

Answer 4

electrical gradient established by ROMK; NKCC reabsorption and paracellular reabsorption happen 50/50

Question 5

what can block the electrical gradient from forming?

Answer 5

loop diuretics

Question 6

in what part of the nephron does the majority of K regulated uptake occur? what types of cells in this area are responsible for the uptake?

Answer 6

CCD/CNT (collecting duct); principal cells

Question 7

what’s the voltage of the principal cell?

Answer 7

-80mV

Question 8

what is the action of the maxi-K (BK) channel? what activates it?

Answer 8

it is an apical K channel; it is activated by depolarization or Ca; the depolarization is canonically brought on by an increase in luminal flow and increased distal Na delivery

Question 9

how do the CCT and CNT reabsorb K?

Answer 9

via H/K ATP-ases, that can increase in number when hypokalemic

Question 10

how can apical K flux change? what four factors can increase or decrease it?

Answer 10

K channel openness and open probability
cellular K conc.
luminal K conc.
voltage

Question 11

what are the two principal regulators of K flux?

Answer 11

aldosterone and distal Na delivery

Question 12

how does aldosterone work? what counters its effects?

Answer 12

aldosterone works by increasing the permeability directly (presumably by working on ROMK) and also by increasing the amount of Na uptake from the lumen thereby hyperpolarizing it and causing K to move down the electrical gradient

Question 13

how was the increased Na uptake results in increased potassium excretion theory proven?

Answer 13

by Liddle syndrome in which Nedd4-2 does not properly function

Question 14

at what level of luminal Na is K secretion maxed out?

Answer 14

25-35mM

Question 15

in addition to the depolarizing effects of increased distal delivery of Na, how else does it increase K release?

Answer 15

the increase distal delivery of sodium is accompanied by the increased distal delivery of water, which dilutes the luminal concentration of K, thereby increasing the concentration gradient for K; depolarization causes activation of MaxiK

Question 16

nonabsorbable anions have what effect on distal K reabsorption?

Answer 16

they increase it (more electronegative mostly)

Question 17

what effect does a chronically consuming a diet high in potassium have?

Answer 17

increased surface area on the basolateral principal cell surface membrane

Question 18

what effect does alkalosis have on K secretion?

Answer 18

activates ROMK, the opposite is true for acidosis

Question 19

what are the two main causes of the aldo/distal delivery system to be out of balance?

Answer 19

loop diuretics cause inc. distal delivery with low ECF

adrenal adenomas cause inc. aldosterone regardless of ECF status