Chloride reabsorption

Two routes:

• Paracellular
  * i.e. through tight junction
• Transceullar

 

In proximal tubule

Paracellular route

Reabsorption of water and sodium

--> INCREASED luminal [Cl-]

--> Greater than [Cl-] in peritubular capillaries

--> Diffusion via paracelluar route

NB:

• Occurs after the early portion of proximal tubule because water need to be reabsorbed first before [Cl-] rises.

Transcellular route

• via Cl-base antiporter
• Coupled with Na-H antiporter

Cl-base antiporter

????Powered by gradient of organic base
* [AV6:p81] Rather vague

• Cl- is reabsorbed from lumen
• Base is secreted into lumen

Na-H antiporter

Driven by Na+ gradient

• Na+ is reabsorbed from lumen
• H+ is secreted into lumen

NB:

In addition to coupling with Cl-base antiporter, Na-H is also responsible for

1. Reabsorption of bicarbonate
2. Most of the Na+ reabsorption in proximal tubule

Recycling

In the lumen, base + H+
--> neutral form of acid
--> diffuses out of lumen back into cells

Overall effect

A "virtual" Na-Cl SYMPORTER

i.e. Na+ and Cl- are cotransported out of lumen into cells

Loop of Henle

• Active reabsorption
  * via Na-K-2Cl symporter

 

Distal convoluted tubule

• Active reabsorption
  * via Na-Cl symporter

Collecting duct

In principle cells

• Cl- reabsorption
  * via paracellular route
  * Passive

In type B intercalated cells

• Cl- reabsorption
  * via apical Cl-HCO3 antiporter
  * Secondary active

In type A intercalated cells

• [AV6:p160]????Cl- secretion