Table 2. Interstitial concentrations (in mM, unless stated otherwise).

Solute	Cortex	OM-IM boundary	Papillary tip
Na+	140.0	299.0	239.0
K+	4.0	8.0	15.0
Cl−	100.0	280.4	236.5
${\text{HCO}}_3^{-}$	25.0	25.0	25.0
${\text{H}}_2{\text{CO}}_3^{-}$	4.41 × 10−3	4.41 × 10−3	4.41 × 10−3
CO2	1.45	1.45	1.45
${\text{HPO}}_4^{2-}+{\text{H}}_2{\text{PO}}_4^{-}$	1.45	1.45	1.45
urea	5.0	60.0	200
${\text{NH}}_3+{\text{NH}}_4^{+}$	1.0	3.9	8.95
${\text{HCO}}_2^{-}+{\text{H}}_2{\text{CO}}_2$	1.0	1.0	1.0
glucose	5.0	6.25	7.5
protein	2.0	2.0	2.0
pH (dimensionless)	7.4	7.4	7.3
osmolality (mosm/(kg H2O))	285.9	688.5	737.9

OM-IM boundary: at the junction between the outer and inner medulla.