Receptor mobility and its cooperative restriction by ligands.
The functional significance of membrane fluidity and receptor mobility in lymphoid cells has been studied in the recent literature. Although far from clarified, the role of membrane fluidity in achieving control over cell activity is probably important; it allows cooperative interactions over long distances. Here, the emphasis is put on the phenomenon of restriction of receptor mobility by ligands such as Concanavalin A, a phenomenon discovered in recent years using morphological techniques. We discuss in some detail our own approach for studying this phenomenon. This consists of quantitatively measuring the active sites on cell-bound lectin molecules by subsequent fixation of horse-radish peroxidase. This study has shown a cooperative binding of Concanavalin A to cells which corresponds to a modification of the membrane, leading to the recruitment of new receptors. The existence of a post-binding event, that we have called micro-redistribution, has been shown at 4 degrees C, through the use of peroxidase binding to cell-bound lectin. A cooperative restriction of receptor microredistribution is observed when the cooperative recruitment of receptors induced by increasing concentrations of Concanavalin A occurs. Both phenomena were shown to be modulated by drugs such as colchicine and cytochalasin B. The characteristics of this modulation suggest that density and distribution of receptors are dependent upon the state of a multimeric submembrane structure which is still functional at 4 degrees C.