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