Redistribution of plasma membrane proteins by electroosmosis elicits cytosolic calcium response in tumor mast cells.

Activation of mast cells and basophils by binding of ligands that crosslink and micro-aggregate cell surface receptors leads to a series of responses including a phosphoinositide cascade, elevation of intracellular free calcium ([Ca2+]i), morphological changes in the cell plasma membrane, and ultimately, exocytosis of granules containing histamine and other mediators of the allergic response. In rat basophilic leukemia (RBL) cells, a tumor mast cell line, stimulation by immunoglobulin E receptor crosslinking induces these responses. In order to determine whether redistribution or aggregation of cell surface proteins is sufficient to induce a response in these cells without extrinsic crosslinking, we have redistributed cell surface proteins by electroosmotic segregation and looked for second messenger [Ca2+]i responses. Video imaging of calcium ion activity using the fluorescent calcium sensitive dye fura-2 revealed the effects of receptor motion and aggregation induced by application of small (10 V/cm) electric fields. A synchronous, monotonic rise in [Ca2+]i generally occurs within a few minutes after a steady field has been applied, while the redistribution of surface proteins is still in progress. The oscillations in [Ca2+]i characteristic of antigen-stimulated cells are not seen, nor are any effects observed in weak alternating fields (0.02, 60 Hz). The observed rise in [Ca2+]i induced by static electric fields is attributed to perturbation of [Ca2+]i regulation by the large-scale redistribution of membrane constituents induced by surface electroosmosis.