The acidic microclimate layer in the vicinity of the cell surface of m
ammalian jejunum is important for absorption of some nutrients, such a
s small peptides and folate. The present study was undertaken to inves
tigate the effect of aging on the cell surface pH (microclimate pH) of
the jejunum of rats. The microclimate pH was measured in vitro in sup
erfused preparations using single-barreled pH-sensitive microelectrode
s filled with a liquid ion exchanger. The thickness of the microclimat
e layer was estimated by reading the distance of microelectrode advanc
ements. The existence of a microclimate pH in the jejunum was confirme
d in the senescent rats, but the value of the microclimate pH was sign
ificantly higher in the senescent (24 mo) rats (6.52 +/- 0.02) than in
the young-adult (6 mo) rats (6.09 +/- 0.01) (P < 0.01). Na+ removal f
rom the perfusate or the addition of amiloride elevated the pH in the
senescent rats as well as in the young-adult rats. The microclimate la
yer was slightly thinner in the senescent rats than in the young-adult
rats. The acidity of the microclimate layer of intestinal surface is
lower in senescent animals than in young-adult ones. One of reasons fo
r this is the thinner mucus layer in senescent animals.