Glutamate and kainate receptors induced by rat brain messenger RNA in Xenopus oocytes

Abstract

Xenopus laevis oocytes injected with poly(A)+ mRNA extracted from rat brain became sensitive to serotonin, glutamate, kainate, acetylcholine and gamma-aminobutyrate. Application of these substances to mRNA-injected oocytes elicited membrane currents. The glutamate- and acetylcholine-induced currents usually showed oscillations, while the kainate current was smooth. The current oscillations during glutamate application reversed direction at about the chloride equilibrium potential (-24 mV), but the reversal potential for the kainate current was close to 0 mV. The current-voltage relation for the glutamate-induced current oscillations showed strong rectification at hyperpolarized potentials, while that for the kainate current was nearly linear. In some oocytes, glutamate elicited smooth membrane currents, with oscillations either absent, or appearing after a delay. The reversal potential of this component was close to 0 mV, and was clearly different from that of the oscillatory component. The appearance of glutamate and kainate sensitivity in the oocyte membrane is due to the translation of the foreign messenger RNA, and not to activation of the oocytes' own genome, because oocytes still become sensitive when transcription is prevented by enucleation or by treatment with actinomycin D. It appears that mRNA from rat brain contains translationally active messengers which code for various neurotransmitter receptors. When this mRNA is injected into Xenopus oocytes, the messengers are translated and receptors are inserted into the oocyte membrane, where they form functionally active receptor-channel complexes.