Characteristics of glycine receptors expressed by embryonic rat brain mRNAs

A study was made of glycine (Gly) and gamma -aminobutyric acid (GABA) recep tors expressed in Xenopus oocytes injected with rat mRNAs isolated from the encephalon, midbrain, and brainstem of 18-day-old rat embryos. In oocytes injected with encephalon, midbrain, or brainstem mRNAs, the Gly-current amp litudes (membrane current elicited by Gly; 1 mM Gly) were respectively 115 +/- 35, 346 +/- 28, and 389 +/- 22 nA, whereas the GABA-currents (1 mM GABA ) were all less than or equal to 40 nA. Moreover, the Gly-currents desensit ized faster in oocytes injected with encephalon or brainstem mRNAs. The EC5 0 for Gly was 611 +/- 77 muM for encephalon, 661 +/- 28 muM for midbrain, a nd 506 +/- 18 muM for brainstem mRNA-injected oocytes, and the correspondin g Hill coefficients were all approximate to2. Strychnine inhibited all of t he Gly-currents, with an IC50 of 56 +/- 3 nM for encephalon, 97 +/- 4 nM fo r midbrain, and 72 +/- 4 nM for brainstem mRNAs. During repetitive Gly appl ications, the Gly-currents were potentiated by 1.6-fold for encephalon, 2.1 -fold for midbrain, and 1.3-fold for brainstem RNA-injected oocytes. Raisin g the extracellular Ca2+ concentration significantly increased the Cry-curr ents in oocytes injected with midbrain and brainstem mRNAs. Reverse transcr iption-PCR studies showed differences in the Gly receptor (GlyR) cu-subunit s expressed, whereas the P-subunit was present in all three types of mRNA. These results indicate differential expression of GlyR mRNAs in the brain a reas examined, and these mRNAs lead to the expression of GlyRs that have di fferent properties. The modulation of GlyRs by Ca2+ could play important fu nctions during brain development.