Tunicamycin alters channel gating characteristics of junctional and extrajunctional acetylcholine receptors expressed in Xenopus oocytes

Tunicamycin decreases the probability of single-channel openings for N-methyl-D-aspartate and alpha-amino-3-hydroxy-5-methyl-4-isoxazole propionic acid receptors

In whole-cell patches from cultured rat hippocampal neurons, tunicamycin (0.1-30 microM), an inhibitor of protein N-glycosylation, depressed currents through N-methyl-D-aspartate and alpha-amino-3-hydroxy-5-methyl-4-isoxazole propionic acid receptor channels in a concentration-dependent manner. Tunicamycin shifted the agonist concentration-response curve for each receptor type to the right. In an outside-out patch-clamp configuration, tunicamycin reduced the number of single-channel opening events in parallel with prolonged mean shut time, without affecting the slope conductance for both the receptors. These tunicamycin effects were obtained with acute treatment, suggesting an action independent of any blockage of N-glycosylation. Tunicamycin, thus, may modify the agonist binding affinity of N-methyl-D-aspartate and alpha-amino-3-hydroxy-5-methyl-4-isoxazole propionic acid receptors, thereby causing a decrease in the probability of single-channel openings leading to the depression of whole-cell membrane currents.

Tunicamycin inhibits NMDA and AMPA receptor responses independently of N-glycosylation

In a whole-cell patch-clamp configuration, currents through N-methyl-D-aspartate (NMDA) and alpha-amino-3-hydroxy-5-methyl-4-isoxazole propionic acid (AMPA) receptor channels were monitored in cultured rat hippocampal neurons, and those currents were depressed to 25 and 28% of basal levels, respectively, by 3-min treatment with tunicamycin (10 microM), an inhibitor of protein N-glycosylation. Tunicamycin (10 microM) reduced amplitude of population spikes elicited in the dentate gyrus of rat hippocampal slices, reaching 78% of basal levels 60 min after the beginning of treatment, and long-term potentiation (LTP) of the perforant path was never induced in the presence of tunicamycin. Tunicamycin, thus, appears to serve as a modulator for NMDA and AMPA receptors, regardless of N-glycosylation, thereby inhibiting neurotransmission and LTP in the dentate gyrus.

Glycosylation of proteins during a critical time window is necessary for the maintenance of long-term potentiation in the hippocampal CA1 region

This paper focuses on the role of glycoproteins in activity-dependent synaptic plasticity. The effect of the different inhibitors of protein glycosylation, Tunicamycin, Brefeldin A and Swainsonine, on long-term potentiation was studied in the CA1 region of rat hippocampal slices. Bath application of the inhibitors 60 min before and during tetanization did not interfere with the induction of long-term potentiation of the field excitatory postsynaptic potential. However, the potentiation in inhibitor-treated slices decreased to baseline levels during 90-180 min. Significant differences in the potentiation in non-treated slices were detectable 80 min (Tunicamycin), 60 min (Brefeldin A) and 75 min (Swainsonine) after tetanization, thus indicating the prevention of long-term potentiation maintenance. The application of Swainsonine 120 and 240 min after tetanization did not influence the potentiated field excitatory postsynaptic potential. These data demonstrate the need for undisturbed glycoprotein processing in a time window around long-term potentiation induction to maintain later phases of long-term potentiation and essential functional implications of protein glycosylation in mechanisms underlying synaptic plasticity.