The proton pump H+-K+-ATPase is the final common pathway mediating the prod
uction and secretion of hydrochloric acid by gastric parietal cells. The pr
esent studies were undertaken to examine whether the expression of gastric
H+-K+-ATPase mRNA and protein changes are associated with the development o
f H+-K+-ATPase activity in the rat fundic gland. H+-K+-ATPase activity was
examined in rat fundic gland at different stages from gestational day 18.5
to postnatal 8 weeks. The expression of H+-K+-ATPase mRNA was detected by i
n situ hybridization using a digoxigenin-labelled RNA probe with a tyramide
signal amplification system. The expression of H+-K+-ATPase protein was ev
aluated by immunoblotting and immunohistochemistry using antibodies against
H+-K+-ATPase alpha- and beta -subunits. We found that H+-K+-ATPase enzyme
activity was detectable from the onset of gland formation (day 19.5 of gest
ation) and increased with age in the developing rat fundic gland. Expressio
n of mRNA and protein was also discernible at the same time, and a progress
ive increase in expressions was observed as rats developed. Our results sug
gested that in developing rat fundic gland, the expression of both mRNA and
protein of H+-K+-ATPase increased with age in a manner that parallels the
development of H+-K+-ATPase enzymebreak activity.