Objectives: Elevated expression of the Na⁺/H⁺ exchanger NHE1 has been proposed to contribute to increased migratory and invasive properties in cancer (1). The Na⁺,HCO₃^- - cotransporter NBCn1, which also exerts net acid extrusion, could in principle exert the same effects, but this was never investigated. An N- terminally truncated, constitutively active ErbB2 receptor (DNErbB2) is common in human breast cancer and associated with increased malignancy. Here we investigate the roles of NHE1 and NBCn1 in migration, adhesion and invasion of MCF-7 breast cancer cells in the presence or absence of DNErbB2. Methods: Transporter localization was assessed by immunofluorescence analysis, migration of serum- starved cells on collagen I, adhesion measured on basal lamina and collagen I, and invasion in basal lamina- or collagen I-coated Boyden chambers. Results: NHE1 and NBCn1 were evenly distributed in the plasma membrane in absence of DNErbB2. Upon DNErbB2 expression, NHE1 predominantly localized to lamellipodium-like protrusions, and NBCn1 predominantly to cell- cell contacts. Migration velocity increased by 30% upon DNErbB2 expression. Inhibition of NHE1 (EIPA, 10 mM) and NBCn1 (S0859, 10 mM) had no effect on velocity in the absence of DNErbB2. However, in DNErbB2 expressing cells velocity was increased by 25% by NHE1 inhibition and modestly reduced by NBCn1 inhibition. Furthermore, EIPA enhanced adhesion of DNErbB2 expressing cells to collagen I and basal lamina, and reduced invasion of DNErbB2 expressing cells through collagen I and basal lamina. Conclusion: DNErbB2 expression in MCF-7 cells elicited increased 2D motility and non-uniform plasma membrane distribution of NHE1 and NBCn1, by yet unknown mechanisms. Migration velocity was modestly reduced by inhibition of NBCn1. In contrast, NHE1 inhibition increased migration velocity, and augmented adhesion to, yet inhibited invasion through, collagen I and basal lamina. 1) Gatenby, R.A., Gillies, R.J. Nat Rev Cancer 8: 56-61, 2008