The association between acidification and electrogenic events in the rat proximal jejunum

Abstract

Simultaneous measurement of H+ production, transmural potential difference and intermittent short-circuit current (SCC) was made in the rat proximal jejunum in vitro. Similarly, K+ and Na+ movements were measured to investigate the relationship of acidification to electrogenic events and associated ion movements in the jejunum. Acidification correlated significantly with the short-circuit current and both were inhibited by 10 mM serosal ouabain or 10 mM mucosal aminophylline. Both inhibitors had effects on net K+ movement but not on net Na+ movement. Moreover, in isotope studies whereas 10 mM serosal ouabain reduced the Jms Na+ flux, 10 mM mucosal aminophylline had no effect, i.e., aminophylline can reduce both short-circuit current and acidification without perceptibly altering the serosally directed Na+ flux. In low-Na buffers in which acidification still occurs although reduced, transmural potential differences occur of reversed polarity that are apparently unrelated to Na diffusion potential differences (as evidenced by isotopic Na efflux experiments) and which could be caused by H+ production. In low Na+ buffers the inhibitors have opposing effects, ouabain causing an increase and aminophylline a decrease in the reversed potential differences. A model for acidification (that of K+ rather than Na+ exchange for the H+ and hydroxyl for Cl- exchange) is proposed to explain the present experimental findings and other diverse observations in the literature. Although either step might be the electrogenic step, acidification must be also considered as a component of the jejunal short-circuit current.