Lumen

Luminal -

membrane

Nat-K+ ATPase

1

Primary active Nat and K+ transport

Blood

Na

Nat

145

mmol/L

Basolateral membrane

Na

15

mmol/L

2

4[Na*] = Chemical driving force for Nat

Nat

-70 m/

-70 mV

3

Back diffusion of K+

creates membrane potential

-70 mV

4

#Membranepotential

= electrical driving force for Nat