Is there a Cl−−OH− exchange (Cl−−H+ cotransport) mechanism in the brush-border membrane of the intestine of the fresh water trout (Salmo gairdneri, R.)?

Abstract

Summary. Experiments were performed to determine the presence of a CI--OH-exchange (C1--H + cotransport) in the brushborder membranes isolated from the intestinal epithelium of freshwater trout. Determinations of alkaline phosphatase activities have shown that vesicle suspensions had an enrichment factor of about 17 in this enzyme indicating a high degree of purification of the brush-border membrane preparation. C1-uptake by vesicles in the presence of a proton gradient occurs against a concentration gradient with an overshoot ratio of about 2 and is inhibited by SITS. Several lines of evidence suggest that the mechanism involved is electrical in nature: (i) CI uptake is increased when the proton gradient is increased, but there is a linear relationship between the C1-uptake and the Nernst potential of protons. (ii) CI-uptake is increased when a proton ionophore is added at low concentration and inhibited at high concentration, suggesting that a proton conductance is involved in the C1-uptake. (iii) there is a linear relationship between the initial speed of the uptake of increasing C1-concentrations and the C1-concentration. (iv) C1-uptake can be modulated by different potassium gradients with or without valinomycin. It is concluded that the enterocyte of the freshwater trout is not equipped with a CI--OH-exchange and the C1-uptake by vesicles is realized by a C1-conductance.Key Words trout 9 intestine 9 brush-border membrane, vesicle 9 C1-conductance