Collecting duct principal cell (V2 receptor)
Target gland or tissue · V2 cAMP Aquaporin-2
Vasopressin binds the basolateral V2 receptor, raises cAMP and PKA, and shuttles preformed aquaporin-2 vesicles into the apical membrane. It also raises inner medullary urea transport, sharpening the gradient the water follows.
Traced from the start
- Supraoptic and paraventricular magnocellular neurones
- Posterior pituitary — vasopressin release
- Collecting duct principal cell (V2 receptor)
Detail
- Channels
- AQP2 is apical and regulated; AQP3 and AQP4 are basolateral and constitutive
- Range
- Urine osmolality can be varied from about 50 to 1200 mOsm/kg
- Requires
- An intact medullary concentration gradient — loop diuretics abolish it and therefore blunt concentrating ability
When it goes wrong
Long-term lithium
Vasopressin resistance (nephrogenic diabetes insipidus): dilute polyuria that does not respond to desmopressin; amiloride is the usual treatment
Hypercalcaemia or hypokalaemia
Acquired concentrating defect with polyuria, reversible once the electrolyte is corrected
Tolvaptan or demeclocycline
V2 blockade used to raise sodium in SIADH resistant to fluid restriction
Practise this structure
1 question in the bank tagged Water Balance.