Lateral transport on cell membranes: mobility of concanavalin A receptors on myoblasts.

Abstract

The lateral mobility of fluorescent labeled concanavalin A receptor complexes was measured on the plasma membrane of cultured rat embryo myoblasts. Transport rates were measured by observing the recovery of fluorescence in a small region of the cell surface initially photobleached irreversibly by an intense, focused laser light pulse. Under different conditions, effective diffusion coefficients (D) of the receptor complexes were measured in the range 8 .times. 10-12 .ltoreq. D .ltoreq. 3 .times. 10-11 cm2/s which is 2 orders of magnitude lower than for a fluorescent lipid probe, D .simeq. (8 .+-. 3) .times. 10-9 cm2/s. This large difference and the presence of apparently immobile concanavalin A receptors suggests that factors beyond the fluidity of the phospholipid bilayer membrane matrix control the rate of lateral transport of the complexes. Effective mobilities of the complexes decrease with increases in the valence, dose and occupation time of the lectin on the membrane. These properties imply an aggregation of the lectin-receptor complexes. Mobilities are not influenced by azide, colchicine or preincubation at low temperature. Cytochalasin B and low temperatures, during the time of measurement, decrease the lateral transport rate.