Mechanisms of Cl- uptake through brush border membranes isolated from the posterior intestine of the freshwater trout, Oncorhynchus mykiss, R.

This paper presents a study of the mechanisms of Cl- transport through the brush border membranes of the posterior part of the intestine in the freshwater trout, Oncorhynchus mykiss. The mechanisms for Cl- transport in the posterior intestine are distinct from those in the middle intestine; an inwardly directed pH gradient stimulates Cl- uptake by brush border membrane vesicles, indicating a Cl-/OH- exchange. A pH-regulated Cl- conductance is present, which is not activated at normal intracellular pH. Cl- uptake is stimulated by an outwardly directed HCO3- gradient revealing the presence of a Cl-/HCO3- exchange but, conversely, Cl- is not exchanged against SO4(2-). In addition, carbonic anhydrase activities have been detected in both the intracellular and extracellular leaflets of the brush border membranes which favour the establishment of a bicarbonate gradient. A model of Cl- transport mechanisms through the brush-border membranes of the posterior intestine of the freshwater trout is proposed.