Responses to GABA, Glycine and β - alanine Induced in Xenopus Oocytes by Messenger RNA from Chick and Rat Brain

Poly (A)⁺ messenger RNA (mRNA) was extracted from rat and chick brains, and injected into oocytes of Xenopus laevis. This led to the expression of receptors that evoked membrane currents in response to γ - aminobutyric acid (GABA), glycine and β - alanine. These currents all inverted at about the chloride equilibrium potential in the oocyte, and showed a marked rectification at negative potentials. Oocytes injected with mRNA from chick optic lobe gave large responses to GABA and β - alanine, but small responses to glycine. In contrast, one fraction of mRNA from rat cerebral cortex (obtained by sucrose density gradient centrifugation) caused oocytes to develop sensitivity to GABA, glycine and β - alanine, whereas a different fraction induced sensitivity to glycine and β - alanine, but very little to GABA. The pharmacological properties of the three amino acid responses also differed. Barbiturate and benzodiazepines potentiated the responses to GABA and β - alanine, but not to glycine. Strychnine reduced the responses to glycine and β - alanine, but not to GABA, whereas bicuculline reduced the responses to GABA and β - alanine, but not to glycine. We conclude that different species of mRNA code for receptors to GABA and glycine, and possibly also for separate β - alanine receptors.