A possible link between active transport of electrolytes and nonelectrolyes.

Abstract

6 pieces of experimental evidence are presented to support the hypothesis that all active intestinal transport mechanisms are dependent on sodium and that this dependence is most likely caused by a critical intracellular sodium concentration that is essential for the conversion of chemical energy into pumping energy. First in the absence of sodium ions active transport of intestinal nonelectrolytes is diminished. Second this inhibition is reversible by replacing sodium ions in the infusion solution. Third the degree of active transport inhibition caused by lack of sodium ions depends on whether sodium is replaced by a substance which rapidly penetrates the mucosal epithelium. Fourth the need for sodium ions for pump functioning is nonspecific for sugar transport. Fifth those systems which have only carrier mechanisms for sugar transport without active pump operate independently of the presence of sodium. And sixth if absorption in the intestine in driven mainly by large lumen-blood concentration differences (i.e. carrier-mediated rather than active pump) sodium is not necessary in the system.