Table 8. Potassium gradients (mM) assumed in the model.

	Top OM	border OM/IM	Bottom IM
MTAL	2.8	26
Interstitium	4.4		34

Potassium assumptions based on [13, 14, 66, 67]. Potassium concentrations are defined at the entry and exit of the medullary thick ascending limbs (MTAL) and interstitium, and elsewhere linearly interpolated. At the entry of the collecting ducts, potassium concentration is initialized at 20mM and is included in the calculation of osmotic pressure (potassium flow is assumed to be constant in this tube, so its concentration increases as volume flow decreases along the CD) as in [17].