Quantitative Methods for Studying the Mobility and Distribution of Receptors on Viable Cells

Abstract

The rapid two-dimensional motion of membrane receptors provides an efficient mechanism for communication among various receptors and for assembly of multi- molecular structures in the plane of the membrane. There is now good evidence that the lateral motion of receptor molecules plays an important physiological role in a number of systems. A relationship between receptor motion and aggregation and biological response has been most convincingly demonstrated in the degranulation of mast cells and basophils. (Ishizaka and Ishizaka, 1971). It was shown that the F_c receptor for immunoglobulin E (I_gE) is monovalent and that the IgE-receptor complex can diffuse in the plane of the membrane with diffusion coefficient D~3 × 10⁻¹⁰ cm² sec⁻¹ (Mendoza and Metzger, 1976; Schlessinger et al., 1976b). The degranulation of mast cells and basophils can be provoked in three different ways; by cross linking IgE-receptor complexes with anti-IgE antibodies (Sirganian et al., 1975); by binding chemically cross-linked IgE dimers to receptors (Segal et al., 1974); by crosslinking the (unoccupied) F_c receptors with divalent anti-receptor antibodies (Isersky et al., 1978). These results indicate that aggregation of the IgE receptors (presumably due to diffusional encounters between receptors) provides the signal for triggering degranulation, and that the ‘unit signal’ results from forming a dimer of receptors.