1. Receptor-mediated endocytosis in epithelial cells is a crucial mechanism
for transport of macromolecules and regulation of cell-surface protein exp
ression. Na+-H+ exchanger type 3 (NHE3) has been shown to cycle between the
apical plasma membrane and the early endosomal compartment and to interfer
e with endocytosis.
2. In the present study we investigated in detail the NHE3-dependent step o
f apical endocytosis in an epithelial cell line (opossum kidney cells).
3. Inhibition of NHE3 led to a rapid dose-dependent inhibition of apical al
bumin endocytosis but did not affect basolateral transferrin endocytosis. R
e-exocytosis of albumin was not increased by NHE3 inhibition.
4. NHE3 dependency of albumin endocytosis was still observed at 20 degreesC
or when microtubules had been disrupted. This was not the case for inhibit
ion of vacuolar H+-ATPase.
5. NHE3 inhibition rapidly blocked internalisation of pre-hound albumin and
attenuated degradation of internalised albumin without changing general pr
6. Furthermore, NHE3 inhibition reduced the rate of endocytic vesicle fusio
7. In summary, our data indicate that NHE3 is important for the early phase
of the apical endocytic pathway, located between the plasma membrane and e
arly endosomes, at least in part due to its involvement in endocytic vesicl