Concanavalin A inhibits oral regeneration in Stentor coeruleus through a mechanism involving binding to the cell surface.

Concanavalin A (Con A) has been shown to induce delays in oral regeneration in the ciliate Stentor coeruleus. Associated with the delayed oral regeneration is a shedding of the cell's extracellular pellicle with the loss of some pigment granules. It is shown that the delays in oral regeneration are not the result of the pigment shedding. The delays are localized in the earliest stages of oral regeneration prior to stage 4. The delays caused by Con A are completely reversible by the addition of 2 mg/ml alpha-D-methyl mannoside either at the time of Con A exposure or 5 min later. Con A clearly binds to the cell surface as shown by the binding of FITC-Con A and its reversal by alpha-methyl mannoside. Crosslinking of Con A receptor molecules may be responsible for the effects of Con A since succinyl Con A, which does not crosslink these receptors, has no effect on oral regeneration even at double the Con A concentration. Calcium ions are also implicated in the action of Con A because an excess of extracellular calcium (10 mM) completely eliminates the Con A delays when added simultaneously with Con A. Examination of the minimum extracellular calcium concentration required for this effect showed that 2 mM calcium can reverse most of the delays but that 5 mM is necessary to completely reverse the delays caused by Con A. If the addition of calcium is delayed for various times after Con A addition, the extracellular calcium is progressively less effective in reversing the Con A delays.