Sodium-coupled amino acid and sugar transport by Necturus small intestine. An equivalent electrical circuit analysis of a rheogenic co-transport system.

Abstract

Necturus small intestine actively absorbs sugars and amino acids by Na-coupled mechanisms that result in increases in the transepithelial electrical potential difference (ψms) and the short-circuit current (Isc) which can be attributed entirely to an increase in the rate of active Na absorption. Studies employing conventional microelectrodes indicate that the addition of alanine or galactose to the mucosal solution is followed by a biphasic response. Initially, there is a rapid depolarization of the electrical potential difference across the apical membrane (ψms) which reverses polarity (i.e. cell interior becomes positive with respect to the mucosal solution) and a marked decrease in the ratio of the effective resistance of the mucosal membrane to that of the serosal membrane (Rm/Rs); these events do not appear to be dependent on the availability of metabolic energy. These initial, rapid events are followed by a slow increase in (Rm/Rs) toward control values which is paralleled by a repolarization ofψms and increases inψms andIsc; this slow series of events is dependent upon the availability of metabolic energy.