Relations of weak-electrolyte transport and acid-base metabolism in rat small intestine in vitro.

The jejunal and ileal regions of rat small intestine in vitro exhibit different patterns of weak-electrolyte transport and acid-base metabolism. The jejunal pattern of weak-electrolyte transport is net transport of weak acids M yields S and of weak bases S yields M (M, mucosal; S, serosal), and the pattern of acid-base metabolism is luminal acidification and serosal alkalinization. In the absence of sodium or in the presence of metabolic inhibitors, weak-electrolyte transport and serosal alkalinization are inhibited, but luminal acidification is not inhibited. The ileal pattern of weak-electrolyte transport is the opposite of that of the jejunum and may be associated with the presence of a luminal alkalinization process observed in this region. In the absence of chloride the ileal patterns of weak-electrolyte transport and acid-base metabolism become similar to those of the jejunum. It is suggested that these observations support a previously proposed model for weak-electrolyte transport in the intestine consisting of a series three-compartment system in which the pH of the intermediate compartment is greater than that of the bulk phases.