Mapping the binding site mediating carisoprodol’s direct activation of GABAA receptors

Carisoprodol (CSP) is a centrally-acting prescription muscle relaxant that can directly activate and allosterically modulate the GABAA receptor. GABAA receptors are the target of many different clinically prescribed compounds. Our previous studies have shown that CSP differentially potentiates GABAA receptor subtypes via allosteric modulation and direct activation. It has been reported that a single amino acid residue, L415, located at the top of the fourth transmembrane domain (TM4) in the a1-subunit of the GABAA receptor is critical to CSP’s direct gating effect. However, whether the residue is involved in CSP binding remains unsolved. The purpose of the present study is to explore the binding site mediating CSP’s direct action with in-silico docking, site-directed mutagenesis and whole-cell electrophysiology. Initial simulated docking of CSP at the GABAA receptor suggested that the CSP binding pocket may be formed by residues from the TM4, pre-TM1 and cys-loop regions of the a-subunit. In whole-cell electrophysiology studies, specific modifications of CSP’s molecular structure produced greater direct action on GABAA receptors. The role of the residues predicted as a CSP binding site in docking analysis are being verified with mutagenesis and patch clamp studies. It is expected that the results will not only enhance our understanding of CSP pharmacology but also the structure-function relationship at the GABAA receptor.