EFFECTS OF AGING ON THE MICROCLIMATE PH OF THE RAT JEJUNUM

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.