Profiling of GABA A and GABA B receptor expression in the myometrium of the human uterus.

Aims: γ-aminobutyric acid (GABA) mediates its physiological effects through the GABA _A and GABA _B receptors. In this study the putative expression of GABA _A R and GABA _B R subunits in human myometrium tissue was investigated.
Main Methods: The expression levels of the 19 GABA _A R subunits (α ₁ -α ₆ , β ₁ -β ₃ , γ ₁ -γ ₃ , δ, ε, π, θ, ρ ₁ -ρ ₃ ) and the three GABA _B R subunits (GABA _B1a , GABA _B1b , GABA _B2 ) were characterized by RT-qPCR analysis on two commercial samples and six samples derived from surgically removed myometrial tissues from different women. We probed for functional GABA _A R expression in primary human myometrial smooth muscle cells (HMSMCs) by whole-cell patch-clamp electrophysiology.
Key Findings: The absolute mRNA levels of the 22 GABA _A R and GABA _B R genes varied considerably across the eight samples, but a pronounced overlap existed between the specific subunits detected in the samples, with α ₂ , β ₂ , β ₃ , ε, π, θ, GABA _B1a and GABA _B1b mRNAs being detected in most samples. The expression profile of GABA _A R and GABA _B R subunit mRNAs in HMSMCs correlated with that observed in the eight tissue samples, albeit the subunit transcripts were detected at lower relative levels. Neither muscimol nor GABA evoked significant currents in these cells in the patch-clamp recordings.
Significance: While the expression of the GABA _B1 subunits on their own is unlikely to give rise to functional GABA _B R expression, the GABA _A R subunits identified at mRNA level would be able to form functional receptors in the human myometrial tissue. Although GABA _A R-mediated currents could not be recorded from HMSMCs in this study, this suggests a role for GABAergic transmission in the human myometrium.
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