[Relationship between Na+ and monosaccharide influx across the microvilli membrane depending on the energy state of the intestinal mucosa wall]

Abstract

1. An energy dependence of the Na+ influx and of the "extra-Na+ influx" across the microvilli membrane was demonstrated in an in vitro preparation of the rat jejunum by adjustment of low ATP/ADP quotients. The monosaccharide influx does not show this dependence. 2. The similar relationship of monosaccharide-dependent Na+ influx and Na+ influx without monosaccharide with the energy state in the mucosa cells suggests a common control system. 3. A constant stoichiometry between monosaccharide and "extra-Na+ influx" can be maintained only under constant intracellular conditions. 4. The changes of the Na+ and K+ influxes by so-called Na+ dependently transported monosaccharides correspond to those which can be elicited by lowering the ATP/ADP ratio in the in vitro preparation. 5. A mechanism is discussed in which an ATP-utilizing reaction is stimulated in the microvilli owing to the monosaccharide transport, thus locally discontinuing the condition for uncoupling of an (Na, K)-ATPase and eliciting an "extra-Na+ influx".