Transport of sulphate in rat jejunal and rat proximal tubular basolateral membrane vesicles

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Abstract
Basolateral membrane vesicles were isolated by a Percoll density gradient centrifugation method from small intestinal and renal proximal tubular epithelial cells. Transport of sulphate across the basolateral membrane was analyzed by measuring the uptake of tracer sulphate. In both membrane preparations, preloading the vesicles with sulphate-or hydroxyl-anions stimulated tracer sulphate uptake (trans-stimulation); an inwardly directed sodium gradient did not stimulate sulphate influx whether in the absence or in the presence of sulphate- or hydroxyl-iontrans-stimulation. Under sulphate trans-stimulation conditions, DIDS (10−4 mol/l) inhibited sulphate influx. In intestinal membranes, trans-stimulation of sulphate influx was obtained by preloading the vesicles with chloride, in renal membranes by preloading with bicarbonate. Under sulphate trans-stimulation conditions, in intestinal membranes, sulphate influx was strongly inhibited by chloride, in renal membranes, chloride inhibition was absent. Under bicarbonate trans-stimulation conditions, in renal membranes, sulphate transport was inhibited by lactate. It is concluded that small intestinal and renal proximal tubular basolateral membrane vesicles contain a transport mechanism for sulphate that cannot be energized by a sodium gradient. The transport system in small intestinal basolateral membranes seems to be different from that in renal membranes. It is suggested that the observed interaction between inorganic and organic anion transport in renal basolateral membranes is indirect.

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