AQP2 and Hyponatremia: The fact that excessive renal water reabsorption and hyponatremia in SIADH, congestive heart failure, liver cirrhosis and preeclampsia coincide with elevated plasma membrane abundance of AQP2, whereas dehydration and hypernatremia in congenital and acquired forms of nephrogenic diabetes insipidus are due to insufficient plasma membrane abundance of AQP2 underscore the importance of a proper regulation of plasma membrane abundance of AQP2 [2].