Bicarbonate movement across basolateral membrane vesicles from rat jejunum.

The self-orienting Percoll-gradient centrifugation was used to separate basolateral membranes (BLMs) from rat jejunal enterocytes. Bicarbonate uptake into osmotically active BLM vesicles was studied by a rapid filtration technique. The time course of [14C] -labelled bicarbonate uptake was followed for 30 min at 18 degrees C and at pH 8.2. Bicarbonate uptake was fast, not saturable and stimulated by countertransport. This work demonstrates that it is possible to determine bicarbonate flux across BLM vesicles at pH and temperature values close to usual experimental conditions. Together with simple diffusion, bicarbonate would cross the BLM of the enterocyte via a carrier-mediated diffusion process.