Calcium transport by permeabilised rabbit small intestinal epithelial cells

Abstract

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 3.6×10⁻⁷ 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 hoth 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 nonmitochondrial compartment. Non-differentiated crypt cells scemed to handle intracellular Ca²⁺ in a similar way as mafure villus cells, although they appeared to buffer at a level about 2×10⁻⁷ M lower.