Printed in Great Britain © Company of Biologist! Limited AN INTRACELLULAR POOL OF A CELL-SURFACE LIGAND WHICH INHIBITS LECTIN-INDUCED CAPPING

It has previously been established that cells dissociated from, embryonic chick neural retina tissues redistribute their cell surface Concanavalin A receptors into patches and caps upon treatment with the lectin. During 4 h in continuous culture the cell population progressively loses the capacity to cap Con A receptors. In the presence of cycloheximide this decrease occurs for only the first 2 h of incubation. Concomitant with this loss in the ability to redistribute Con A receptors, cells become agglutinable by a tissue-specific component first described in 1975. The results of our experiments assaying inhibition of capping by tissue culture supernatant solutions and I09S of capping ability through cellular repair processes are interpreted in terms of an endogenous pool of one or more species, which, when displaced to the cell surface, inhibit the capping of Con-A receptors and permit tissue-specific cell agglutination. Once present at the cell surface, these species are released into the culture medium, either during continuous culture or during an incubation in fresh medium containing cycloheximide. Subsequent to release of these species, the cells regain their capacity for cap formation and lose agglutinability. In addition, the components released from the cells inhibit capping of Con A receptors when added to freshly dissociated cells. The assay methods were also used to determine parameters governing mobilization of the pool of capping inhibitors to the cell surface