ATP6ap2 (pro-renin receptor) is considered to play an important role in the renin-angiotensin system, by acting as an activator of prorenin and as a receptor for both renin and prorenin stimulating ERK1/2 phopshorylation. In addition, ATP6ap2 may be an accessory subunit of the V-type H⁺ ATPase (V-ATPase) regulating cellular and systemic acid-base homeostasis. The aim of the present study is to examine the role of ATP6ap2 in renal V-ATPase function. First we tested if prorenin could regulate V-ATPase function via Atp6ap2. MDCK cells treated with prorenin (1nM) either in the presence or absence of angiotensin receptor 1 and 2 antagonists showed no change in phospho-ERK1/2 levels. Furthermore, addition of prorenin (20 pM or 1 nM) to outer medullary collecting ducts (OMCD) did not stimulate V-ATPase activity. In order to investigate the renal localization of ATP6ap2 and its colocalization with V-ATPases, we examined the mRNA expression of ATP6ap2 and the V-ATPase B1 subunit along the mouse nephron using quantitative RT-PCR and found that these two mRNAs are expressed at high levels in OMCD, cortical collecting duct and connecting tubule. I mmunohistochemistry for ATP6ap2 and various V-ATPase subunits showed that these proteins colocalize in many nephron segments (e.g. intercalated cells and proximal tubule). Hence, our data suggests a possible role for ATP6ap2 for V-ATPase function in the kidney; however, it appears that prorenin does not acutely regulate V-ATPase function via its receptor ATP6ap2 in the kidney.