On the Orientation of Foreign Neurotransmitter Receptors in Xenopus Oocytes

Xenopus oocytes can be made to incorporate into their membrane foreign neurotransmitter receptors and voltage-activated sodium channels. In their original location the receptors are normally activated by the extracellular action of transmitter substances. Tests were made to see if some of the newly synthesized foreign receptors were inserted in the oocyte membrane with their active site facing inwards. Since intracellular injections of acetylcholine, $\gamma $-aminobutyric acid, serotonin and kainic acid and tetrodotoxin into the oocyte failed to elicit a response, we conclude that very few, or none, of the receptor molecules expressed in the oocyte by the exogenous mRNA are inserted with the wrong orientation in the membrane.