Module 5.2 - Chloride Transport Mechanisms

Question 1

Describe the chloride gradient in immature neurons and almost all other cells.

Answer 1

internal [cl] about equal to external [Cl]

Question 2

How do some mature neurons differ in their Cl gradients?

Answer 2

Some actively extrude Cl from cytoplasm such that [Cl-] out&raquo_space; [Cl-]in

Question 3

How do you end up with high [Cl-] in?

Answer 3

Co-transporters use Na gradient to move Cl- into the cell

Question 4

What are the two Cl- co-transporters that move Cl- into the cell?

Answer 4

NCC - Na/Cl Cotransporter
NKCC - Na/K/Cl Cotransporter

Question 5

Describe the ion exchange in NCC.

Answer 5

1 Na+ and 1 Cl- into the cell

Question 6

Describe the ion exchange in NKCC.

Answer 6

transports 1 Na+, 1 K+ and 2 Cl- into cell

Question 7

How do NCC and NKCC differ from NCX and NCKXX?

Answer 7

NCC and NKCC are electrically neutral

Question 8

What needs to happen in order to make a neuron excitable via Cl- channel activation?

Answer 8

Need NCC or NKCC to produce approximately equal Cl- concentrations inside and outside of the cell

Question 9

How many NCC genes do mammals have?

Answer 9

1

Question 10

Name the NCC mammalian gene.

Answer 10

solute carrier 12 A3 (SLC12A3)

Question 11

How many NKCC genes do humans have?

Answer 11

2

Question 12

List the human NKCC genes.

Answer 12

NKCC1/SLC12A2
NKCC2/SLC12A1

Question 13

How do you end up with a lower internal Cl- concentration?

Answer 13

Cotransporters that us the K+ gradient move Cl- out of the cell

Question 14

Name the cotransporter that moves Cl- out of the cell

Answer 14

KCC - K+/Cl- cotransporter

Question 15

Describe the ion exchange of KCC. Is it electrically neutral

Answer 15

1 K and 1 Cl out of cell
Yes

Question 16

What needs to happen for a neuron to be hyperpolarized via Cl- channel activation?

Answer 16

KCC needs to produce [Cl-] in &laquo_space;[Cl-] out

Question 17

How many KCC genes are present in mammals?

Answer 17

4

Question 18

List the 4 mammalian KCC genes.

Answer 18

SLC12A4/KCC1
SLC12A5/KCC2
SLC12A6/KCC3
SLC12A7/KCC4

Question 19

Describe the role Cl- co-transport plays in pH regulation. (4)

Answer 19

Na-dependent Cl-/HCO3- exchange system uses Na+ gradient to move bicarbonate into the cell and protons out
HCO3- is part of a physiological buffering system crucial in nervous system, where cells have little tolerance for pH changes
Higher cytoplasmic [H+] promotes H+ efflux and HCO3- influx
Increase in [HCO3-] then shifts the equation to the left, further neutralizing cytoplasmic pH.