The 16-kD subunit of the vacuolar H+-ATPase (V-ATPase), or ductin, is essen
tial for the activity of this proton pump and has roles in intercellular co
mmunication and control of cell growth and differentiation. The V-ATPase is
important for acidification-dependent degradation of tissue matrices throu
gh which some cell types move, and for pH regulation across some epithelial
cell layers. Placentation involves intricate signaling, cell proliferation
, and controlled invasion. We examined the distribution of three subunits o
f the V-ATPase in bovine trophoblast and endometrium at the time of implant
ation to determine the relationship of ductin expression to that of two oth
er subunits, A (approximately 73 kD) and B (approximately 58 kD). Epithelia
l expression of all three subunits was observed, and in nonpregnant animals
this expression was apical. As pregnancy proceeded, expression of all subu
nits became pericellular in luminal but not glandular epithelium, suggestin
g a redistribution of V-ATPase activity. The trophoblast expressed all thre
e subunits during initial contact with the epithelium. In the stroma, ducti
n expression was reduced after implantation, and we discuss the possibility
that ductin plays a role in the shifting communication between stromal and
epithelial cells induced by embryo attachment.