EFFECTS OF CONCANAVALIN-A ON DESENSITIZATION KINETICS OF GABA RESPONSES IN ACHATINA-FULICA NEURONS

The effects of the lectin concanavalin A (Con A), on the kinetics of d esensitization of the responses of voltage clamped Achatina fulica LP5 neuron to microperfused acetylcholine (ACh) and GABA were compared. B oth ACh and GABA elicited increases in chloride conductance which deca yed biphasically during prolonged applications of these agonists; an i nitial rapid decay was followed by a later slow decay. Con A (5 mu g/m l) accelerated both the fast and the slow decays of responses to ACh. Con A (5 mu g/ml) also accelerated the fast decay of responses to GABA , but the slow decay was unaffected even by 20 mu g/ml or more of the lectin. It is suggested that, at least in the case of GABA receptor, t he fast and slow decays involve distinct desensitization kinetics. The effects of Con A on the desensitization of the ACh and GABA responses were reversed by D-mannose, a competitive and specific inhibitor of C on A binding to membrane sugar residues. These results provide further evidence that receptor desensitization can be influenced by perturbin g the sugar moieties associated with the subunits comprising these sig nalling macromolecules. The carbohydrate residues may play an importan t role in regulating desensitization of transmitter receptors.