Table 1.

Key Proteins Involved in Regulation of Water Balance.

Protein	Gene	Structure or Cell Type Relevant to Water Balance	Manifestation of Loss of Function*	Drugs That Target Protein
Arginine vasopressin	AVP	NeuNeurons of supraoptic nucleus and paraventricular nucleus	Central diabetes insipidus	None
Vasopressin receptor
V2	AVPR2	RenRenal thick ascending limb of the loop of Henle, distal convoluted tubule, connecting tubule, collecting duct	X-linked nephrogenic diabetes insipidus	DesmDesmopressin acetate (agonist), tolvap- tan (antagonist)
V1a	AVPRlA	RenRenal medullary vasculature (vasa recta)	None	Conivaptan (nonselec- tive V1a and V2 antagonist)
BumeBumetanide-sensitive sodi- um-potassium–chlo–ride cotransporter	SLCl2Al	RenRenal thick ascending limb of the loop of Henle	Type I Bartter’s syndrome	Loop Loopdiuretics
ThiaziThiazide-sensitive sodium- chloride cotransporter	SLCl2A3	RenRenal distal convoluted tubule	Gitelman’s syndrome	Thiazide diuretics
Aquaporin
Aquaporin-1	AQPl	Renal proximal tubule, thin descending limb of the loop of Henle, erythrocyte	Colton blood group-null	None
Aquaporin-2	AQP2	RenRenal connecting tubule, collecting duct	Autosomal nephrogenic diabetes insipidus	None
Aquaporin-3	AQP3	RenRenal connecting tubule, collecting duct, erythrocyte	GIL blood group-null	None
Aquaporin-4	AQP4	RenRenal connecting tubule, collecting duct	None	None
Vasopressin-regulated urea channel	SLCl4A2	RenRenal inner medullary collecting duct, thin descending limb of the loop of Henle	None	None
Epithelial sodium channel
Beta subunit	SCNNlB	RenRenal connecting tubule, collecting duct	Type I pseudohypoaldoster- onism	Amiloride
Gamma subunit	SCNNlG	RenRenal connecting tubule, collecting duct	Type I pseudohypoaldoster- onism	Amiloride

^*Data are from the Online Mendelian Inheritance in Man database.