K+ Channels in Epithelial function

Question 1

Function of K+ channels?

Answer 1

Maintain resting membrane potential
Help set up the driving force for the secretion of Cl-
Regulate cell volume!!

Question 2

Voltage gated K+ channels –> features?

Answer 2

6 tmds, 4 sub units, 1 pore region, 1 voltage sensor. ‘Kv’ !!

Question 3

Inwardly rectifying K+ channels –> features?

Answer 3

2 tmds, 4 sub units, 1 pore region, ‘Kir family’

Question 4

2 pore K+ channels?

Answer 4

4 tmds, 2 sub units, 2 pore regions, ‘2p family’

Question 5

Channels found in the upper airway?

Answer 5

Kv - KCNE1/E2/E3, KCNQ1
Kir - 1.1 - ROMK !!
2pore - Twik1/ Twik2

Question 6

Role of K+ channels in the upper airway model?

Answer 6

K+ channels maintain the Cl- gradient (for Cl- secretion) –> when the K+ channel becomes activated, this causes hyperpolarisation, which drives Cl- secretion (Cl- ions brought in by NKCC2) –> K+ channel and Cl- channel active at the same time!!

Question 7

What inhibits the KCNQT1 protein (channel?)

Answer 7

Chromanol 329B

Question 8

CULTURED NASAL CELLS AND BRONCHIAL CELLS –> results when C329B added?

WHat about when Ba2+ is added?

Answer 8

Inhibits K+ channels and therefore inhibits Cl- secretion –> this is shown by a smaller short circuit current (ussing chamber used) and less negative Transepithelial potential

Once Ba2+ added –> almost all current blocked –> other K+ channels involved too!!

Question 9

CF vs non CF - what is the impact of Forskolin/IBMX (causes increase in cAMP)
What about the production of Ba2+-sensitive K+ channels?

Answer 9

• less activation of channels upon addition of Forskolin/IBMX in CF cells
• less production of Ba2+ sensitive K+ channel currents (normally drives Cl- secretion)

Question 10

Regulation of Basolateral K+ channel - regulated by ? what does this result in?

Answer 10

E3 sub unit regulates it and is cAMP activated! Activated and drives Cl- secretion

Question 11

What is HSK4 and where is it found?

Answer 11

Basolateral K+ found in the upper airway –> activated by Ca2+ and blocked by CLOTRIMAZOLE
Supports Cl- secretion!!!

Question 12

What is Cacc and where is it found?

Answer 12

Apical Cl- channel –> activated by Ca2+/UTP and stimulates K+/Cl- secretion.
Without this channel CF patients would be even more ill – upregulating this channel alleviates some of the symptoms of CF

Supports Cl- secretion!!!

Question 13

BK channel - where is it found? activated by?

K.D cells of BK - observations?

Answer 13

LARGE CONDUCTANCE+ channel in the apical membrane –> ATP/Ca2+ activated
Decrease in ATP-activated s.s.c (Cl- currents)

Question 14

What blocks BK channels ? Evidence?

Answer 14

PAXILINE –> channel blocker –> inhbit Cl- secretion by causing a decrease in response to ATP on the apical membrane

Question 15

What are the links between channels in epithelial cells?

Answer 15

HSK4 and Cacc channel via ic [Ca2+]

KVLQT1 + CFTR via levels of cAMP

Question 16

When K+ (c329) inhibited and HSK4 inhibited (Clotramizole) what is shown in patients with CF

Answer 16

INCREASED INHIBITION OVERALL SEEN (decreased SSC) –> already not working properly

Question 17

BK channels and cilia beat frequency –> impact of Paxilline on this ?
Results of knock down?

Answer 17

• prevents cells ability to set height of liquid layer –> prevents cilia functioning
• knocks down cilia beat frequency to around 0 –> cells cannot set PCL at the correct height when this channel isnt functioning!!!