Calcium transport by permeabilised rabbit small intestinal epithelial cells.

Intestinal epithelial cells isolated from rabbit small intestine and whose plasma membrane had been rendered highly permeable were used to study the role of intracellular structures in Ca2+ buffering. Monitoring free Ca2+ with a selective electrode revealed that the cells could reduce Ca2+ concentration in the medium to a level of 3.6 X 10(-7) M independently, within a certain range, of the initial Ca2+ concentration or amount of cells used. Ca2+ buffering by permeabilised enterocytes was Mg2+- and ATP-dependent and was abolished in the presence of the Ca2+ ionophore A23187. The rapidity of Ca2+ buffering, but not the final Ca2+ level attained, was reduced in the combined presence of the mitochondrial inhibitors azide and oligomycin or in the presence of ruthenium red. Buffering of Ca2+ was abolished in the presence of vanadate, although some uptake was still observed. Complete blocking occurred in the presence of both vanadate and mitochondrial inhibitors. Measurement of initial rates of uptake with radioactive calcium revealed that mitochondrial uptake plays a role at relatively high Ca concentrations but that at the presumably physiological levels most of the uptake is into a non-mitochondrial compartment. Non-differentiated crypt cells seemed to handle intracellular Ca2+ in a similar way as mature villus cells, although they appeared to buffer at a level about 2 X 10(-7) M lower.