3. Old stuff
          3.2. Old physio stuff (around 2005)
              3.2.3. Physiology
                  3.2.3.12. Renal
                      3.2.3.12.5. Renal handling of organic substances
 3.2.3.12.5.1. Active secretions of organic anions and cations 

Active secretions of organic anions and cations

Active secretion of organic anions in proximal tubules

Transport from ISF into tubular epithelial cells
* By active transporters in basolateal membrane
* Rate-limiting step

--> Exit into lumen
* By facilitated diffusion
* Via uniporters or sodium-dependent antiporters

Also a Tm system.

Examples

  • Bile salts
    * i.e. glucuronate or sulfate conjugates
  • Hydroxybenzoates
  • Fatty acids
  • PAH
  • Oxalate
  • Prostaglandins
  • Urate
Drugs
  • Acetazolamide
  • Chlorothiazide
  • Ethacrynate
  • Furosemide
  • Penicillin
  • Probenecid
  • Saccharin
  • Salicylates
  • Sulfonamides

 

Urate

  • Not protein-bound
    --> Freely filterable
  • Almost all filtered urate are reabsorbed early in the proximal tubule
  • Then later on actively secreted in proximal tubules, then reabsorbed again later
  • Overall --> reabsorption
  • Controlled to maintain relatively constant plasma level

 

Active secretion of organic cations in proximal tubules

Transport from ISF into tubular epithelial cells
* By uniporters

--> Exit into lumen
* By antiporter (exchange with H+)

Also a Tm system

Examples

Acetylcholine

Choline

Creatinine

Dopamine

Epinephrine

Guanidine

Histamine

Serotonin

Norepinephrine

Thiamine

Drugs

Atropine

Isoproterenol

Cimetidine

Meperidine

Morphine

Procaine

Quinine

Tetraethyl ammonium