Concanavalin A increases N-methyl-D-aspartate-induced Ca2+ influx in cerebellar granule cells in culture

Desensitization of glutamatergic receptors can be inhibited by various endogenous and/or exogenous agents e.g. by lectins. Effect of lectin, concanavalin A (con A) on N-methyl-D-aspartate (NMDA)-induced Ca2+ influx was studied in cultured cerebellar granule cells. Additionally the effect of con A on 3H-(+)-5-methyl-10,11-dihydro-5H-dibenzocyclohepten-5,10-imine maleate (3H-(+)MK-801) binding to NMDA receptors was investigated. Preincubation with con A enhanced NMDA efficacy (but not potency) to stimulate Ca2+ influx. The potency of MK-801 to inhibit NMDA effect was similar in both control and con A pretreated cells. Preincubation of cortical membranes with con A resulted in a robust decrease of Bmax 3H-MK-801 binding and modest decrease in affinity. This contradiction between Ca2+ influx and binding experiments may result from the difference in the subtype of NMDA receptors or different expression of con A action in both assays.