Effect of tunicamycin on the expression of functional brain neurotransmitter receptors and voltage-operated channels in Xenopus oocytes.

The role of N-glycosylation on the expression of functional brain neurotransmitter receptors and voltage-operated channels was studied by injecting Xenopus oocytes with mRNA from rat brain or chick optic lobe, and culturing them in the presence or absence of tunicamycin, an inhibitor of asparagine linked glycosylation. Electrophysiological recordings were then made to assess the amounts of functional receptors and channels present in the oocyte membrane. The appearance of gamma-aminobutyric acid (GABA) receptors and voltage-activated Na+ channels was profoundly reduced. In contrast, the functional expression of kainate receptors, and voltage-activated K+ and Ca2+ channels was much less affected. Thus, it seems that kainate receptors, and K+ and Ca2+ channels can be expressed and function normally without being glycosylated. On the other hand, GABA receptors and Na+ channels may need to be N-glycosylated in order to function properly, or to ensure their correct insertion into the membrane.